PL/SQL CONDICIONALES Y CICLOS

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Copyright © 2020, Oracle and/or its affiliates. All rights reserved.
Database Programming with
PL/SQL
4-1
Conditional Control: IF Statements

3
PLSQL 4-1
Conditional Control: IF State
Objectives
•This lesson covers the following objectives:
−Describe a use for conditional control structures
−List the types of conditional control structures
−Construct and use an IF statement
−Construct and use an IF-THEN-ELSE statement
−Create PL/SQL to handle the null condition in IF statements
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PLSQL 4-1
Purpose
•In this section, you learn how to use the conditional
logic in a PL/SQL block
•Conditional processing extends the usefulness of
programs by allowing the use of simple logical tests to
determine which statements are executed
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5
PLSQL 4-1
Purpose
•Think of a logic test as something you do every day
•If you get up in the morning and it is cold outside, you
will choose to wear cold-weather clothing
•If you get up in the morning and it is warm outside, you
will choose to wear warm-weather clothing
•And if there is a chance of rain, then you will bring a
rain coat or an umbrella with you
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The IF statement contains alternative courses of action in a block based on conditions. A condition
is an expression with a TRUE or FALSE value that is used to make a decision.
The CASE statement contains alternative courses of action in a block based on one condition. They
are different in that they can be used outside of a PLSQL block in a SQL statement.
LOOPs are control structures that allow iteration of statements. Loop control structures are
repetition statements that enable you to execute statements in a PLSQL block repeatedly. There
are three types of loop control structures supported by PL/SQL—BASIC, FOR, and WHILE.
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PLSQL 4-1
Controlling the Flow of Execution
•You can change the logical flow of statements within
the PL/SQL block with a number of control structures
•This lesson introduces three types of PL/SQL control
structures:
−Conditional constructs with the
IF statement
−CASE expressions
−LOOP control structures
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FOR
LOOP
WHILE

Writing in pseudocode combines natural language with code-like elements. It is sometimes used
when introducing new structures and concepts. Pseudocode generally excludes syntax
requirements and adds words that capture the logic of the structure/concept under consideration.
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PLSQL 4-1
IF Statement
•The IF statement shown below using "pseudocode"
contains alternative courses of action in a block based
on conditions
•A condition is an expression with a TRUE or FALSE
value that is used to make a decision
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if the region_id is in (5, 13, 21)
then print "AMERICAS"
otherwise, if the region_id is in (11, 14, 15)
then print "AFRICA"
otherwise, if the region_id is in (30, 34, 35)
then print "ASIA"
Conditions

CASE expressions will be discussed more fully in a future lesson.
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PLSQL 4-1
CASE Expressions
•CASE expressions are similar to IF statements in that
they also determine a course of action based on
conditions
•They are different in that they can be used outside of a
PLSQL block in an SQL statement
•Consider the following pseudocode example:
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if the region_id is
5 then print "AMERICAS"
11 then print "AFRICA"
30 then print "ASIA" …

Loops will be discussed more fully in a future lesson.
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PLSQL 4-1
LOOP Control Structures
•Loop control structures are repetition statements that
enable you to execute statements in a PLSQL block
repeatedly
•Three types of loop control structures are supported by
PL/SQL: BASIC, FOR, and WHILE
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FOR
LOOP
WHILE

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PLSQL 4-1
LOOP Control Structures
•Consider the following pseudocode example:
−Print the numbers 1–5 by using a loop and a counter
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Loop Counter equals: 1
Statement processed.
FOR
LOOP
WHILE

Please note the ELSIF does not have an 'E' after the 'S,' and there is no space. There can be many
ELSIF clauses within an IF statement. There can be only one ELSE clause within an IF statement
(and it comes just before the END IF). Also, each THEN clause within the IF statement ends with a
semicolon.
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PLSQL 4-1
IF Statements Structure
•The structure of the PL/SQL IF statement is similar to
the structure of IF statements in other procedural
languages
•It enables PL/SQL to perform actions selectively based
on conditions
•Syntax:
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IF condition THEN
statements;
[ELSIF condition THEN
statements;]
[ELSE
statements;]
END IF;

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PLSQL 4-1
IF Statements
•Condition is a Boolean variable or expression that
returns TRUE, FALSE, or NULL
•THEN introduces a clause that associates the Boolean
expression with the sequence of statements that
follows it
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IF condition THEN
statements;
statements;]
[ELSE
statements;]
END IF;

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PLSQL 4-1
IF Statements
•Statements can be one or more PL/SQL or SQL
statements
•They can include further IF statements containing
several nested IF, ELSE, and ELSIF statements
•The statements in the THEN clause are executed only if
the condition in the associated IF clause evaluates to
TRUE
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IF condition THEN
statements;
statements;]
[ELSE
statements;]
END IF;

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PLSQL 4-1
IF Statements
•ELSIF is a keyword that introduces an additional
Boolean expression
•If the first condition yields FALSE or NULL, then the
ELSIF keyword introduces additional conditions
•ELSIF is the correct spelling, not ELSEIF
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IF condition THEN
statements;
statements;]
[ELSE
statements;]
END IF;

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PLSQL 4-1
IF Statements
•ELSE introduces the default clause that is executed if,
and only if, none of the earlier conditions (introduced
by IF and ELSIF) are TRUE
•The tests are executed in sequence so that a later
condition that might be true is pre-empted by an
earlier condition that is true
•END IF; marks the end of an IF statement
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IF condition THEN
statements;
statements;]
[ELSE
statements;]
END IF;

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PLSQL 4-1
IF Statements Note
•ELSIF and ELSE are optional in an IF statement
•You can have any number of ELSIF keywords but only
one ELSE keyword in your IF statement
• END IF marks the end of an IF statement and must be
terminated by a semicolon
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IF condition THEN
statements;
statements;]
[ELSE
statements;]
END IF;

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PLSQL 4-1
Simple IF Statement
•This is an example of a simple IF statement with a
THEN clause
•The v_myage variable is initialized to 31
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DECLARE
v_myage NUMBER := 31;
BEGIN
IF v_myage < 11
THEN
DBMS_OUTPUT.PUT_LINE('I am a child');
END IF;
END;

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PLSQL 4-1
Simple IF Statement
•The condition for the IF statement returns FALSE
because v_myage is not less than 11
•Therefore, the control never reaches the THEN clause
and nothing is printed to the screen
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DECLARE
BEGIN
IF v_myage < 11
THEN
END IF;
END;

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PLSQL 4-1
IF THEN ELSE Statement
•The ELSE clause has been added to this example
•The condition has not changed, thus it still evaluates to
FALSE
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DECLARE
v_myage NUMBER:=31;
BEGIN
IF v_myage < 11
THEN
ELSE
DBMS_OUTPUT.PUT_LINE('I am not a child');
END IF;
END;

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PLSQL 4-1
IF THEN ELSE Statement
•Remember that the statements in the THEN clause are
only executed if the condition returns TRUE
•In this case, the condition returns FALSE, so control
passes to the ELSE statement
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DECLARE
v_myage NUMBER:=31;
BEGIN
IF v_myage < 11
THEN
ELSE
END IF;
END;

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PLSQL 4-1
IF ELSIF ELSE Clause
•The IF statement now contains multiple ELSIF clauses
as well as an ELSE clause
•Notice that the ELSIF clauses add additional conditions
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PLSQL 4-1
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DECLARE
BEGIN
IF v_myage < 11
THEN
ELSIF v_myage < 20
THEN
DBMS_OUTPUT.PUT_LINE('I am young');
ELSIF v_myage < 30
THEN
DBMS_OUTPUT.PUT_LINE('I am in my twenties');
ELSIF v_myage < 40
THEN
DBMS_OUTPUT.PUT_LINE('I am in my thirties');
ELSE
DBMS_OUTPUT.PUT_LINE('I am mature');
END IF;
END;
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PLSQL 4-1
•As with the IF statement, each ELSIF condition is
followed by a THEN clause
•This is executed only if the ELSIF condition returns
TRUE
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PLSQL 4-1
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DECLARE
BEGIN
IF v_myage < 11
THEN
ELSIF v_myage < 20
THEN
DBMS_OUTPUT.PUT_LINE('I am young');
ELSIF v_myage < 30
THEN
DBMS_OUTPUT.PUT_LINE('I am in my twenties');
ELSIF v_myage < 40
THEN
DBMS_OUTPUT.PUT_LINE('I am in my thirties');
ELSE
DBMS_OUTPUT.PUT_LINE('I am mature');
END IF;
END;
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The IF clause now contains multiple ELSIF clauses and an ELSE clause. Observe that the ELSIF
clauses have conditions, but the ELSE clause has no condition. The condition for ELSIF should be
followed by the THEN clause that is executed if the condition of the ELSIF clause returns TRUE.
When you have multiple ELSIF clauses, if the first condition is FALSE or NULL, the control shifts to
the next ELSIF clause.
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PLSQL 4-1
•When you have multiple clauses in the IF statement
and a condition is FALSE or NULL, control then passes
to the next clause
•Conditions are evaluated one by one
•If all conditions are FALSE or NULL, then the statements
in the ELSE clause are executed
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PLSQL 4-1
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…IF v_myage < 11 THEN
DBMS_OUTPUT.PUT_LINE(' I am a child ');
ELSIF v_myage < 20 THEN
DBMS_OUTPUT.PUT_LINE(' I am young ');
DBMS_OUTPUT.PUT_LINE(' I am in my twenties ');
DBMS_OUTPUT.PUT_LINE(' I am in my thirties ');
ELSE
DBMS_OUTPUT.PUT_LINE(' I am always young ');
END IF;…
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PLSQL 4-1
•The final ELSE clause is optional
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…IF v_myage < 11 THEN
DBMS_OUTPUT.PUT_LINE(' I am a child ');
DBMS_OUTPUT.PUT_LINE(' I am young ');
DBMS_OUTPUT.PUT_LINE(' I am in my twenties ');
DBMS_OUTPUT.PUT_LINE(' I am in my thirties ');
ELSE
DBMS_OUTPUT.PUT_LINE(' I am always young ');
END IF;…

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PLSQL 4-1
IF Statement with Multiple Expressions
•An IF statement can have multiple conditional
expressions related with logical operators, such as
AND, OR, and NOT
• This example uses the AND operator
•Therefore, it evaluates to TRUE only if both BOTH the
first name and age conditions are evaluated as TRUE
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DECLARE
v_myfirstname VARCHAR2(11) := 'Christopher';
BEGIN
IF v_myfirstname ='Christopher' AND v_myage < 11
THEN
DBMS_OUTPUT.PUT_LINE('I am a child named Christopher');
END IF;
END;

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PLSQL 4-1
IF Statement with Multiple Expressions
•There is no limitation on the number of conditional
expressions that can be used
•However, these statements must be connected with
the appropriate logical operators
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DECLARE
v_myfirstname VARCHAR2(11) := 'Christopher';
BEGIN
IF v_myfirstname ='Christopher' AND v_myage < 11
THEN
DBMS_OUTPUT.PUT_LINE('I am a child named Christopher');
END IF;
END;

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PLSQL 4-1
NULL Values in IF Statements
•In this example, the v_myage variable is declared but is
not initialized
•The condition in the IF statement returns NULL, which
is neither TRUE nor FALSE
•In such a case, the control goes to the ELSE statement
because, just NULL is not TRUE
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PLSQL 4-1
NULL Values in IF Statements
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DECLARE
v_myage NUMBER;
BEGIN
IF v_myage < 11
THEN
ELSE
END IF;
END;
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PLSQL 4-1
Handling Nulls
•When working with nulls, you can avoid some common
mistakes by keeping in mind the following rules:
−Simple comparisons involving nulls always yield NULL
−Applying the logical operator NOT to a null yields NULL
−In conditional control statements, if a condition yields NULL,
it behaves just like a FALSE, and the associated sequence of
statements is not executed
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PLSQL 4-1
Handling Nulls Example
•In this example, you might expect the sequence of
statements to execute because a and b seem equal
•But, NULL is unknown, so we don't know if a and b are
equal
•The IF condition yields NULL and the THEN clause is
bypassed, with control going to the line following the
THEN clause
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a := NULL;
b := NULL;
...
IF a = b THEN … -- yields NULL, not TRUE and the
sequence of statements is not executed
END IF;

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PLSQL 4-1
Guidelines for Using IF Statements
•Follow these guidelines when using IF statements:
−You can perform actions selectively when a specific condition
is being met
−When writing code, remember the spelling of the keywords:
• ELSIF is one word
• END IF is two words
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PLSQL 4-1
Guidelines for Using IF Statements
•If the controlling Boolean condition is TRUE, then the
associated sequence of statements is executed; if the
controlling Boolean condition is FALSE or NULL, then
the associated sequence of statements is passed over
•Any number of ELSIF clauses is permitted
•Indent the conditionally executed
statements for clarity
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• CASE – An expression that determines a course of action based on conditions and can be used
outside of a PL/SQL block in a SQL statement.
• Condition – An expression with a TRUE or FALSE value that is used to make a decision.
• IF – Statement that enables PL/SQL to perform actions selectively based on conditions.
• LOOP– Control structures- Repetition statements that enable you to execute statements in a
PL/SQL block repeatedly.
36
PLSQL 4-1
Terminology
•Key terms used in this lesson included:
−CASE
−Condition
−IF
−LOOP
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PLSQL 4-1
Summary
•In this lesson, you should have learned how to:
−Describe a use for conditional control structures
−List the types of conditional control structures
−Construct and use an IF statement
−Construct and use an IF-THEN-ELSE statement
−Create PL/SQL to handle the null condition in IF statements
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PL/SQL
4-2
Conditional Control: Case Statements

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PLSQL 4-2
Objectives
−Construct and use CASE statements in PL/SQL
−Construct and use CASE expressions in PL/SQL
−Include the correct syntax to handle null conditions in PL/SQL
CASE statements
−Include the correct syntax to handle Boolean conditions in
PL/SQL IF and CASE statements
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4
PLSQL 4-2
Purpose
•In this lesson, you learn how to use CASE statements
and CASE expressions in a PL/SQL block
•CASE STATEMENTS are similar to IF statements, but are
often easier to write and easier to read
•CASE EXPRESSIONS work like functions to return one
value from a number of values into a variable
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PLSQL 4-2
Using a CASE Statement
•Look at this IF statement. What do you notice?
•All the conditions test the same variable v_numvar
•And the coding is very repetitive: v_numvar is coded
many times
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DECLARE
v_numvar NUMBER;
BEGIN
...
IF v_numvar = 5 THEN statement_1; statement_2;
ELSIF v_numvar = 10 THEN statement_3;
ELSIF v_numvar = 12 THEN statement_4; statement_5;
ELSIF v_numvar = 27 THEN statement_6;
ELSIF v_numvar ... – and so on
ELSE statement_15;
END IF; ...
END;

The WHEN clauses, “WHEN 5,” “WHEN 10,” “WHEN 12,” etc. mean: WHEN v_numvar is equal to 5,
and WHEN v_numvar is equal to 10, etc.
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PLSQL 4-2
Using a CASE Statement
•Here is the same logic, but using a CASE statement
•It is much easier to read. v_numvar is written only
once
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DECLARE
v_numvar NUMBER;
BEGIN
...
CASE v_numvar
WHEN 5 THEN statement_1; statement_2;
WHEN 10 THEN statement_3;
WHEN 12 THEN statement_4; statement_5;
WHEN 27 THEN statement_6;
WHEN ... – and so on
ELSE statement_15;
END CASE;
...
END;

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PLSQL 4-2
CASE Statements: An Example
•A simple example to demonstrate the CASE logic
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DECLARE
v_num NUMBER := 15;
v_txt VARCHAR2(50);
BEGIN
CASE v_num
WHEN 20 THEN v_txt := 'number equals 20';
ELSE v_txt := 'some other number';
END CASE;
DBMS_OUTPUT.PUT_LINE(v_txt);
END;

The same logic from above, rewritten using an IF statement:
DECLARE
v_num NUMBER := 15;
v_txt VARCHAR2(50);
BEGIN
IF v_num > 20 THEN v_txt := 'greater than 20';
ELSIF v_num > 15 THEN v_txt := 'greater than 15';
ELSE v_txt := 'less than 16';
END IF;
END;
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PLSQL 4-2
Searched CASE Statements
•You can use CASE statements to test for non-equality
conditions such as <, >, >=, etc.
•These are called searched CASE statements
•The syntax is virtually identical to an equivalent IF
statement
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DECLARE
v_num NUMBER := 15;
v_txt VARCHAR2(50);
BEGIN
CASE
WHEN v_num > 20 THEN v_txt := 'greater than 20';
WHEN v_num > 15 THEN v_txt := 'greater than 15';
ELSE v_txt := 'less than 16';
END CASE;
END;

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PLSQL 4-2
Using a CASE Expression
•You want to assign a value to one variable that
depends on the value in another variable
•Look at this IF statement
•Again, the coding is very repetitive
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DECLARE
v_out_var VARCHAR2(15);
v_in_var NUMBER;
BEGIN
...
IF v_in_var = 1 THEN v_out_var := 'Low value';
ELSIF v_in_var = 50 THEN v_out_var := 'Middle value';
ELSIF v_in_var = 99 THEN v_out_var := 'High value';
ELSE v_out_var := 'Other value';
END IF;
...
END;

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PLSQL 4-2
Using a CASE Expression
•Here is the same logic, but using a CASE expression:
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DECLARE
v_in_var NUMBER;
BEGIN
...
v_out_var := CASE v_in_var
WHEN 1 THEN 'Low value'
WHEN 50 THEN 'Middle value'
WHEN 99 THEN 'High value'
ELSE 'Other value'
END;
...
END;

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PLSQL 4-2
CASE Expression Syntax
•A CASE expression is different from a CASE statement
because it selects one of a number of results and
assigns it to a variable
•A CASE expression ends with END not END CASE
•In the syntax, expressionN can be a literal value or an
expression such as (v_other_var * 2)
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variable_name :=
CASE selector
WHEN expression1 THEN result1
WHEN expression2 THEN result2
...
WHEN expressionN THEN resultN
[ELSE resultN+1]
END;

Answer:
Grade: C
Appraisal: Good
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PLSQL 4-2
CASE Expression Example
•What would be the result of this code if v_grade was
initialized as "C" instead of "A"
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DECLARE
v_grade CHAR(1) := 'A';
v_appraisal VARCHAR2(20);
BEGIN
v_appraisal :=
CASE v_grade
WHEN 'A' THEN 'Excellent'
WHEN 'B' THEN 'Very Good'
WHEN 'C' THEN 'Good'
ELSE 'No such grade'
END;
DBMS_OUTPUT.PUT_LINE('Grade: ' || v_grade ||
' Appraisal: ' || v_appraisal);
END;
RESULT:
Grade: A
Appraisal: Excellent

Answer: "Same value" will be displayed. Remember, read the highlighted WHEN clause as, "When
v_in_var is equal to v_in_var, then assign "Same value" to v_out_var and skip to the line following
the CASE expression end." Since v_in_var is equal to itself, the code will display the phrase, "Same
value."
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PLSQL 4-2
CASE Expression: A Second Example
•Determine what will be displayed when this block is
executed:
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DECLARE
v_in_var NUMBER := 20;
BEGIN
v_out_var :=
CASE v_in_var
WHEN 1 THEN 'Low value'
WHEN v_in_var THEN 'Same value'
WHEN 20 THEN 'Middle value'
ELSE 'Other value'
END;
DBMS_OUTPUT.PUT_LINE(v_out_var);
END;

Searched CASE expressions are more flexible, allowing non-equality conditions (and compound
conditions) to be tested and different variables to be used in different WHEN clauses.
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PLSQL 4-2
Searched CASE Expression Syntax
• PL/SQL also provides a searched CASE expression, which
has the following form:
• A searched CASE expression has no selector
• Also, its WHEN clauses contain search conditions that yield
a Boolean value, not expressions that can yield a value of
any type
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variable_name := CASE
WHEN search_condition1 THEN result1
WHEN search_condition2 THEN result2
...
WHEN search_conditionN THEN resultN
[ELSE resultN+1]
END;

We could have used a non-searched CASE expression. The example in the slide could be written
as:
v_appraisal :=
CASE v_ grade
WHEN ‘A’ THEN ‘Excellent’
WHEN ‘B’ THEN ‘Good’
WHEN ‘C’ THEN ‘Good’
ELSE ‘No such grade’
END;
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PLSQL 4-2
Searched CASE Expressions: An Example
•Searched CASE expressions allow non-equality
conditions, compound conditions, and different
variables to be used in different WHEN clauses
15
DECLARE
BEGIN
v_appraisal :=
CASE -- no selector here
WHEN v_grade = 'A' THEN 'Excellent'
WHEN v_grade IN ('B','C') THEN 'Good'
END;
DBMS_OUTPUT.PUT_LINE ('Grade: '|| v_grade ||
' Appraisal ' || v_appraisal);
END;

CASE expressions are actually functions, which always return exactly one value.
A common, built-in function is SYSDATE. Just like a CASE expression, SYSDATE assigns one value to
a variable.
v_date := SYSDATE;
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PLSQL 4-2
How are CASE Expressions Different From CASE
Statements?
•They are different because:
−CASE expressions return a value into a variable
−CASE expressions end with END;
−A CASE expression is a single PL/SQL statement
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DECLARE
BEGIN
v_appraisal :=
CASE
WHEN v_grade = 'A' THEN 'Excellent'
WHEN v_grade IN ('B','C') THEN 'Good'
END;
DBMS_OUTPUT.PUT_LINE ('Grade: '|| v_grade || ' Appraisal '
|| v_appraisal);
END;

A CASE expression has only one terminating semicolon at the END;, while a CASE statement has a
semicolon after each executable statement in a WHEN clause.
17
PLSQL 4-2
How are CASE Expressions Different From CASE
Statements?
•CASE statements evaluate conditions and perform
actions
•A CASE statement can contain many PL/SQL statements
•CASE statements end with END CASE;
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DECLARE
BEGIN
CASE
WHEN v_grade = 'A' THEN
DBMS_OUTPUT.PUT_LINE ('Excellent');
WHEN v_grade IN ('B','C') THEN
DBMS_OUTPUT.PUT_LINE ('Good');
ELSE
DBMS_OUTPUT.PUT_LINE('No such grade');
END CASE;
END;

You can build a simple Boolean condition by combining number, character, or date expressions
with comparison operators.
You can build a complex Boolean condition by combining simple Boolean conditions with the
logical operators AND, OR, and NOT. The logical operators are used to check the Boolean variable
values and return TRUE, FALSE, or NULL.
Note: The negation of NULL (NOT NULL) results in a null value because null values are
indeterminate.
18
PLSQL 4-2
Logic Tables
•When using IF and CASE statements you often need to
combine conditions using AND, OR, and NOT
•The following Logic Table displays the results of all
possible combinations of two conditions
•Example: TRUE and FALSE is FALSE
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AND TRUE FALSE NULL OR TRUE FALSE NULL NOT
TRUE TRUE
Ex.
FALSE
NULL TRUE TRUE TRUE TRUE TRUE FALSE
FALSE FALSE FALSE FALSE FALSE TRUE FALSE NULL FALSE TRUE
NULL NULL FALSE NULL NULL TRUE NULL NULL NULL NULL

The AND Logic Table on the previous slide can help you evaluate the possibilities for the Boolean
condition in this slide.
Answers:
1. TRUE
2. FALSE
3. NULL
4. FALSE
19
PLSQL 4-2
Boolean Conditions
•What is the value of v_flag in each case?
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v_flag := v_reorder_flag AND v_available_flag;
V_REORDER_FLAG V_AVAILABLE_FLAG V_FLAG
TRUE TRUE 1. _____
TRUE FALSE 2. _____
NULL TRUE 3. _____
NULL FALSE 4. _____

• CASE expression – An expression that selects a result and returns it into a variable.
• CASE statement – A block of code that performs actions based on conditional tests.
• Logic Tables – Shows the results of all possible combinations of two conditions.
20
PLSQL 4-2
Terminology
−CASE expression
−CASE statement
−Logic tables
20

21
PLSQL 4-2
Summary
−Construct and use CASE statements in PL/SQL
−Construct and use CASE expressions in PL/SQL
−Include the correct syntax to handle null conditions in PL/SQL
CASE statements
−Include the correct syntax to handle Boolean conditions in
PL/SQL IF and CASE statements
21

2
PL/SQL
4-3
Iterative Control: Basic Loops

3
PLSQL 4-3
Objectives
−Describe the need for LOOP statements in PL/SQL
−Recognize different types of LOOP statements
−Create PL/SQL containing a basic loop and an EXIT statement
with conditional termination
3

4
PLSQL 4-3
Purpose
•Looping constructs are the second type of control
structure
•Loops are mainly used to execute statements
repeatedly until an EXIT condition is reached
•PL/SQL provides three ways to structure loops to
repeat a statement or a sequence of statements
multiple times
•These are basic loops, FOR loops, and WHILE loops
•This lesson introduces the three loop types and
discusses basic loops in greater detail
4
WARNING:
When a user executes a PL/SQL block in APEX that contains an infinite loop, there is no way for the
user to stop the loop. It can only be stopped by the DBA who oversees the Academy database. If
the loop does not contain DML statements, closing the browser window and reopening it will
allow the user to continue coding. If the block contains a FOR UPDATE clause, the affected table(s)
will remain locked until released by the DBA, which may take a day or more.
Be careful executing loops. All loops required by this course should have some type of limiting
condition. NO infinite loops are required as part of this course.

Each loop is structured for a specific purpose. These loops are used to write code to handle all
situations (problems). Loops can repeat one statement, a group of statements, and/or a block.
Loops have a scope and loop variables have a life.
5
PLSQL 4-3
Iterative Control: LOOP Statements
•Loops repeat a statement or a sequence of statements
multiple times
•PL/SQL provides the following types of loops:
−Basic loops that perform repetitive actions without overall
conditions
−FOR loops that perform iterative actions based on a counter
−WHILE loops that perform repetitive actions based on a
condition
5

6
PLSQL 4-3
Basic Loops
•The simplest form of a LOOP statement is the basic
loop, which encloses a sequence of statements
between the keywords LOOP and END LOOP
•Use the basic loop when the statements inside the
loop must execute at least once
6

7
PLSQL 4-3
Basic Loops Exit
•Each time the flow of execution reaches the END LOOP
statement, control is passed to the corresponding
LOOP statement that introduced it
•A basic loop allows the execution of its statements at
least once, even if the EXIT condition is already met
upon entering the loop
•Without the EXIT statement, the loop would never end
(an infinite loop)
7
BEGIN
LOOP
statements;
EXIT [WHEN condition];
END LOOP;
END;

8
PLSQL 4-3
Basic Loops Simple Example
•In this example, no data is processed
•We simply display the loop counter each time we
repeat the loop
8
DECLARE
v_counter NUMBER(2) := 1;
BEGIN
LOOP
DBMS_OUTPUT.PUT_LINE('Loop execution #' || v_counter);
v_counter := v_counter + 1;
EXIT WHEN v_counter > 5;
END LOOP;
END;

9
PLSQL 4-3
Basic Loops More Complex Example
•In this example, three new location IDs for Montreal,
Canada, are inserted in the LOCATIONS table
9
DECLARE
v_loc_id locations.location_id%TYPE;
BEGIN
SELECT MAX(location_id) INTO v_loc_id FROM locations
WHERE country_id = 2;
LOOP
INSERT INTO locations(location_id, city, country_id)
VALUES((v_loc_id + v_counter), 'Montreal', 2);
END LOOP;
END;

10
PLSQL 4-3
Basic Loops EXIT Statement
•You can use the EXIT statement to terminate a loop
and pass control to the next statement after the END
LOOP statement
•You can issue EXIT as an action within an IF statement
10
DECLARE
v_counter NUMBER := 1;
BEGIN
LOOP
DBMS_OUTPUT.PUT_LINE('Counter is ' || v_counter);
IF v_counter > 10 THEN EXIT;
END IF;
END LOOP;
END;

11
PLSQL 4-3
Basic Loop EXIT Statement Rules
•Rules:
−The EXIT statement must be placed inside a loop
−If the EXIT condition is placed at the top of the loop (before
any of the other executable statements) and that condition is
initially true, then the loop exits and the other statements in
the loop never execute
−A basic loop can contain multiple EXIT statements
11

The statement, EXIT WHEN v_counter > 10, is logically identical to:
IF v_counter > 10 THEN EXIT;
END IF;
However, in PL/SQL, the EXIT WHEN statement is the appropriate syntax. From a programmer's
perspective, it is the more elegant solution.
12
PLSQL 4-3
Basic Loop EXIT WHEN Statement
•Although the IF…THEN EXIT works to end a loop, the
correct way to end a basic loop is with the EXIT WHEN
statement
•If the WHEN clause evaluates to TRUE, the loop ends
and control passes to the next statement following
END LOOP
12
DECLARE
BEGIN
LOOP
DBMS_OUTPUT.PUT_LINE('Counter is ' || v_counter);
END LOOP;
END;

• Basic Loop – A sequence of statements between the keywords LOOP and END LOOP; the
statements must execute at least once.
• Counter – A counter is a variable that programmers use to keep track of the number of times a
loop executes (or repeats). When a specific value is reached, it triggers the execution of the
EXIT command which stops the loop from repeating, passing control to the first command
following the END LOOP command.
• END LOOP – A PL/SQL command that marks the end of the statements within a loop and
returns control to the corresponding LOOP statement that introduced it (the loop begins again).
• EXIT – Statement to terminate a loop.
• LOOP – A PL/SQL command that marks the beginning of the statements within a loop.
13
PLSQL 4-3
Terminology
−Basic Loop
−Counter
−END LOOP
−EXIT
−LOOP
13

14
PLSQL 4-3
Summary
−Describe the need for LOOP statements in PL/SQL
−Recognize different types of LOOP statements
with conditional termination
14

2
PL/SQL
4-4
Iterative Control: WHILE and FOR Loops

3
PLSQL 4-4
Objectives
−Construct and use the WHILE looping construct in PL/SQL
−Construct and use the FOR looping construct in PL/SQL
−Describe when a WHILE loop is used in PL/SQL
−Describe when a FOR loop is used in PL/SQL
3

4
PLSQL 4-4
Purpose
•The previous lesson discussed the basic loop, which
allows the statements inside the loop to execute at
least once
•This lesson introduces the WHILE loop and FOR loop
•The WHILE loop is a looping construct which requires
the controlling condition be evaluated at the start of
each iteration
•The FOR loop should be used if the number of
iterations is known
4

Since the WHILE loop depends on a condition and is not fixed, use the WHILE loop when you don’t
know in advance the number of times a loop must execute.
5
PLSQL 4-4
WHILE Loops
•You can use the WHILE loop to repeat a sequence of
statements until the controlling condition is no longer
TRUE
•The condition is evaluated at the start of each iteration
•The loop terminates when the condition is FALSE or
NULL
•If the condition is FALSE or NULL at the initial execution
of the loop, then no iterations are performed
5
WHILE condition LOOP
statement1;
statement2;
. . .
END LOOP;

6
PLSQL 4-4
WHILE Loops
•In the syntax:
•Condition is a Boolean variable or expression (TRUE,
FALSE, or NULL)
•Statement can be one or more PL/SQL or SQL
statements
6
statement1;
statement2;
. . .
END LOOP;

7
PLSQL 4-4
WHILE
•In the syntax:
•If the variables involved in the conditions do not
change during the body of the loop, then the condition
remains TRUE and the loop does not terminate
•Note: If the condition yields NULL, then the loop is
bypassed and control passes to the statement that
follows the loop
7
statement1;
statement2;
. . .
END LOOP;

Notice the similarities and differences to the basic loop from the previous lesson:
DECLARE
BEGIN
WHERE country_id = 'CA';
LOOP
VALUES((v_loc_id + v_counter), 'Montreal', 'CA');
END LOOP;
8
PLSQL 4-4
WHILE Loops
•In this example, three new location IDs for Montreal,
Canada, are inserted in the LOCATIONS table
•The counter is explicitly declared in this example
8
DECLARE
BEGIN
WHILE v_counter <= 3 LOOP
END LOOP;
END;

9
PLSQL 4-4
WHILE Loops
•With each iteration through the WHILE loop, a counter
(v_counter) is incremented
•If the number of iterations is less than or equal to the
number 3, then the code within the loop is executed
and a row is inserted into the locations table
9

PLSQL 4-4
WHILE Loops
10
DECLARE
BEGIN
END LOOP;
END;
10

11
PLSQL 4-4
WHILE Loops
•After the counter exceeds the number of new locations
for this city and country, the condition that controls the
loop evaluates to FALSE and the loop is terminated
11
DECLARE
BEGIN
END LOOP;
END;

12
PLSQL 4-4
FOR Loops Described
•FOR loops have the same general structure as the basic
loop
•In addition, they have a control statement before the
LOOP keyword to set the number of iterations that
PL/SQL performs
12
FOR counter IN [REVERSE]
lower_bound..upper_bound LOOP
statement1;
statement2;
. . .
END LOOP;

13
PLSQL 4-4
FOR Loop Rules
•FOR loop rules:
−Use a FOR loop to shortcut the test for the number of
iterations
−Do not declare the counter; it is declared implicitly
−lower_bound .. upper_bound is the required syntax
13
statement1;
statement2;
. . .
END LOOP;

14
PLSQL 4-4
FOR Loops Syntax
•Counter is an implicitly declared integer whose value
automatically increases or decreases (decreases if the
REVERSE keyword is used) by 1 on each iteration of the
loop until the upper or lower bound is reached
•REVERSE causes the counter to decrement with each
iteration from the upper bound to the lower bound
• (Note that the lower bound is referenced first)
14
statement1;
statement2;
. . .
END LOOP;

Note these examples for controlling the counter through the FOR loop:
FOR i IN 1..5 LOOP …; -- successive values 1,2,3,4,5
FOR i IN REVERSE 1..5 LOOP …; -- successive values 5,4,3,2,1
FOR i IN REVERSE 5..1 LOOP …; -- will cause an error.
15
PLSQL 4-4
FOR Loops Syntax
•lower_bound specifies the lower bound for the range
of counter values
•upper_bound specifies the upper bound for the range
of counter values
15
statement1;
statement2;
. . .
END LOOP;

16
PLSQL 4-4
FOR Loop Example
•You have already learned how to insert three new
locations for the country code CA and the city
Montreal by using the simple LOOP and the WHILE
loop
•The next slide shows you how to achieve the same by
using the FOR loop
16

PLSQL 4-4
FOR Loop Example
17
DECLARE
BEGIN
FOR i IN 1..3 LOOP
VALUES((v_loc_id + i), 'Montreal', 2);
END LOOP;
END;
17

18
PLSQL 4-4
FOR Loop Guidelines
•FOR loops are a common structure of programming
languages
•A FOR loop is used within the code when the beginning
and ending value of the loop is known
•Reference the counter only within the loop; its scope
does not extend outside the loop
•Do not reference the counter as the target of an
assignment
•Neither loop bound (lower or upper) should be NULL
18

19
PLSQL 4-4
FOR Loop Expression Example
•While writing a FOR loop, the lower and upper bounds
of a LOOP statement do not need to be numeric literals
•They can be expressions that convert to numeric values
19
DECLARE
v_lower NUMBER := 1;
v_upper NUMBER := 100;
BEGIN
FOR i IN v_lower..v_upper LOOP
...
END LOOP;
END;

Note: All loops allow the use of an EXIT WHEN condition allowing the loop to terminate before the
WHILE condition is false or the upper bound of the FOR loop is reached
Remember that all the variables used within the loop block have a scope. The specific loop needed
is determined by the problem being solved.
20
PLSQL 4-4
Guidelines For When to Use Loops
•Use the basic loop when the statements inside the
loop must execute at least once
•Use the WHILE loop if the condition has to be
evaluated at the start of each iteration
•Use a FOR loop if the number of iterations is known
20

• FOR Loop – Repeats a sequence of statements until a set number of iterations are fulfilled.
• Lower Bound – The FOR loop syntax that specifies the lower bound for the range of counter
values.
• REVERSE – A PL/SQL command that causes the FOR loop counter to decrement with each
iteration from the upper bound to the lower bound.
• Upper Bound – The FOR loop syntax that specifies the upper bound for the range of counter
values.
• WHILE Loop – Repeats a sequence of statements until the controlling condition is no longer
TRUE.
21
PLSQL 4-4
Terminology
−FOR loops
−Lower Bound
−REVERSE
−Upper Bound
−WHILE loops
21

22
PLSQL 4-4
Summary
−Construct and use the WHILE looping construct in PL/SQL
−Construct and use the FOR looping construct in PL/SQL
−Describe when a WHILE loop is used in PL/SQL
−Describe when a FOR loop is used in PL/SQL
22

2
PL/SQL
4-5
Iterative Control: Nested Loops

3
PLSQL 4-5
Objectives
−Construct and execute PL/SQL using nested loops
−Label loops and use the labels in EXIT statements
−Evaluate a nested loop construct and identify the exit point
3

4
PLSQL 4-5
Purpose
•You’ve learned about looping constructs in PL/SQL
•This lesson discusses how you can nest loops to
multiple levels
•You can nest FOR, WHILE, and basic loops within one
another
4

The slide example shows a FOR loop nested inside another FOR loop. But (for example) we could
nest a WHILE loop inside a FOR loop; or a FOR loop inside a basic loop; or etc. All combinations
are allowed.
5
PLSQL 4-5
Nested Loop Example
•In PL/SQL, you can nest loops to multiple levels
•You can nest FOR, WHILE, and basic loops within one
another
5
BEGIN
FOR v_outerloop IN 1..3 LOOP
FOR v_innerloop IN REVERSE 1..5 LOOP
DBMS_OUTPUT.PUT_LINE('Outer loop is: ' ||
v_outerloop ||
' and inner loop is: ' ||
v_innerloop);
END LOOP;
END LOOP;
END;

Answer : We will discuss loop labels in the next slides to answer this question.
Notice that when V_INNER_DONE = 'YES', PL/SQL exits the inner loop but the outer loop continues
executing.
6
PLSQL 4-5
Nested Loops
•This example contains EXIT conditions in nested basic
loops
•What if you want to exit from the outer loop at step A?
6
DECLARE
v_outer_done CHAR(3) := 'NO';
v_inner_done CHAR(3) := 'NO';
BEGIN
LOOP -- outer loop
...
LOOP -- inner loop
...
... -- step A
EXIT WHEN v_inner_done = 'YES';
...
END LOOP;
...
EXIT WHEN v_outer_done = 'YES';
...
END LOOP;
END;

7
PLSQL 4-5
Loop Labels
•Loop labels are required in this example in order to exit
an outer loop from within an inner loop
7
DECLARE
...
BEGIN
<<outer_loop>>
LOOP -- outer loop
...
<<inner_loop>>
LOOP -- inner loop
EXIT outer_loop WHEN ... -- exits both loops
...
END LOOP;
...
EXIT WHEN v_outer_done = 'YES'; ...
END LOOP;
END;

8
PLSQL 4-5
Loop Labels
•Loop label names follow the same rules as other
identifiers
•A label is placed before a statement, either on the
same line or on a separate line
•In FOR or WHILE loops, place the label before FOR or
WHILE within label delimiters (<<label>>)
•If the loop is labeled, the label name can optionally be
included after the END LOOP statement for clarity
8

The loop labels are not required in this example, but they do make the code more readable.
9
PLSQL 4-5
Loop Labels
•Label basic loops by placing the label before the word
LOOP within label delimiters (<<label>>)
9
DECLARE
v_outerloop PLS_INTEGER := 0;
v_innerloop PLS_INTEGER := 5;
BEGIN
<<outer_loop>>
LOOP
v_outerloop := v_outerloop + 1;
v_innerloop := 5;
EXIT WHEN v_outerloop > 3;
<<inner_loop>>
LOOP
DBMS_OUTPUT.PUT_LINE('Outer loop is: ' || v_outerloop ||
' and inner loop is: ' || v_innerloop);
v_innerloop := v_innerloop - 1;
EXIT WHEN v_innerloop = 0;
END LOOP inner_loop;
END LOOP outer_loop;
END;

10
PLSQL 4-5
Nested Loops and Labels
•In this example, there are two loops
•The outer loop is identified by the label
<<outer_loop>>, and the inner loop is identified by the
label <<inner_loop>>
•We reference the outer loop in the EXIT statement
from within the
inner_loop
10

PLSQL 4-5
Nested Loops and Labels
11
...BEGIN
<<outer_loop>>
LOOP
<<inner_loop>>
LOOP ...
EXIT outer_loop WHEN v_total_done = 'YES';
-- Leave both loops
-- Leave inner loop only ...
END LOOP inner_loop; ...
END LOOP outer_loop;
END;
11

• Label Delimiters – Characters placed before (<<) and after (>>) a loop label to identify the label
as a loop label.
• Loop Label – A loop identifier that is required in order to exit an outer loop from within an inner
loop.
12
PLSQL 4-5
Terminology
−Label Delimiters
−Loop Label
12

13
PLSQL 4-5
Summary
−Construct and execute PL/SQL using nested loops
−Label loops and use the labels in EXIT statements
−Evaluate a nested loop construct and identify the exit point
13

PL/SQL CONDICIONALES Y CICLOS

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