The document provides an overview of SQL concepts for retrieving and manipulating data using SQL statements like SELECT, JOIN, GROUP BY, and subqueries. It discusses the key clauses and operations for projection, selection, aggregation, sorting, joining tables, grouping data, and using subqueries. Some important points covered include using SELECT to retrieve specific attributes or calculate column values, filtering rows with WHERE, sorting with ORDER BY, aggregation functions, inner/outer/cross joins, and applying grouping and aggregation at different levels with ROLLUP and CUBE.

1. Retrieving Data Using SQL
SELECT Statement
Ms. Amrit Kaur
gamritkaur@live.com

2. 1. PROJECTION OPERATION

3. 1.1 What is Projection?
• Projection of all tuples over some set of
attributes.
• It is used to
– Reduce the degree of relation
– Reorder attributes
– Customizing the display
– Calculating Column Values
• Projection yields vertical subset of relation.

4. 1.1.1 Retrieve Specific Attributes
• SELECT statement is used to retrieve specific
attributes
– Syntax
SELECT column1, column2, .....columnn
[ INTO new_table_name ]
FROM { tablename | viewname }

5. 1.1.2 Customizing the Display
SELECT column1 AS “col_name”, .....
[ INTO new_table_name ]
FROM { tablename | viewname }

6. 1.1.3 Calculating Column Values
• Arithmetic operators are used to show
calculated values for the columns.
• Oracle support following arithmetic operators
• + (for addition)
• - (for subtraction)
• / (for division)
• * (for multiplication)
• % (for modulo)

7. 2. SELECTION OPERATION

8. 2.1 What is Selection?
• Selection over complete set of attributes but
subset of tuples included .
• Only those tuples that satisfied selection
condition included in result set therefore
referred as Restriction operation.
• Selection yields horizontal subset of relation.

9. Selection Operation [contd.]
• WHERE clause in SELECT statement is used to
retrieve selected rows
• Syntax
SELECT column1, column2, .....columnn
[ INTO new_table_name ]
FROM { tablename | viewname }
WHERE search_condition

10. Selection Operation [contd.]
• Selection is based on the following conditions
– Records match one or more condition
– Record contain values in a given range
– Record contain value from a given set of values
– Record that match a pattern
– Record contain NULL Values

11. 2.1.1 Retrieving Selected Row
• Match one or more condition
– Comparison Operators (=, >, <, >=, <=, <>, !=) and
– Logical Operators (AND / OR /NOT) are used.
SELECT column1, column2, .....columnn
[ INTO new_table_name ]
FROM { tablename | viewname }
WHERE condition1 {AND / OR / NOT } condition2

12. 2.1.2 Retrieving Selected Row
• Contain values in a given range
– Range Operator (BETWEEN , NOT BETWEEN ) is
used.
SELECT column1, column2, .....columnn
[ INTO new_table_name ]
FROM { tablename | viewname }
WHERE expression1 range_operator expression2 AND
expression3
• Name of the ColumnNumeric Values

13. 2.1.3 Retrieving Selected Row
• Contain value from a given set of values
– List Operator (IN, NOT IN) is used.
SELECT column1, column2, .....columnn
[ INTO new_table_name ]
FROM { tablename | viewname }
WHERE expression list_operator (value_list)
•Values are separated by comma(,)
•Strings values are enclosed in single inverted commas (‘’)

14. 2.1.4 Retrieving Selected Row
• Match a pattern
– LIKE / NOT LIKE keyword is used to search a string
by using wildcards
– Wildcards used with LIKE keyword are
• % represents any number of characters
• Underscore (_) represents one character

15. 2.1.5 Retrieving Selected Row
• Contain NULL Values
– IS NULL / IS NOT NULL keyword is used.
SELECT column1, column2, .....columnn
[ INTO new_table_name ]
FROM { tablename | viewname }
WHERE coulmn_name {IS NULL | IS NOT NULL}

16. 2.2 Retrieve Sorted Data
• ORDER BY clause of SELECT statement is used
to display the data in specific order.
– Ascending (ASC) or Descending (DESC) order
SELECT column1, column2, .....columnn
[ INTO new_table_name ]
FROM { tablename | viewname }
[WHERE search_condition]
[ORDER BY columnname [ASC / DESC] , colname2
[ASC / DESC] , .....]

17. Retrieve Sorted Data
• The records are sorted in ascending order by
default.
• ORDER BY clause doesn’t sort the table
physically.

18. 3. SELECTION USING FUNCTIONS

19. 3.1 Types of Function
• Scalar or Single Row functions
– Works on single row at a time
– Returns single result for each row
• Group or Aggregate or Multiple Row functions
– Works on multiple row at a time
– Returns a single result for that group

20. 3.2 Scalar Function
• Character Function
• Numeric Function
• Date Function
• Data Type Conversion Function

21. 3.3. Aggregated Function
• Aggregate functions return a single result row
based on groups of rows.
• Used to calculate the summarized values of a
column based on a set of rows.

22. Aggregated Functions
• Aggregated Functions are:
– SUM( [ALL | DISTINCT] expression )
– AVG( [ALL | DISTINCT] expression )
– COUNT( [ALL | DISTINCT] expression )
– COUNT(*)
– MAX(expression)
– MIN(expression)

23. Aggregated Functions
• DISTINCT
– cause an aggregate function to consider only
distinct values of the argument expression.
• ALL
– causes an aggregate function to consider all
values, including all duplicates.

24. 4. JOIN OPERATION

25. Join
• Join allows combining of two or more table to
form a single new relation.
• More than one tables can be join based on
common attributes.
• A join is implemented using SELECT statement,
FROM clause specify table names and WHERE
clause specify join condition.

26. • When inner join is applied, only rows with
values that satisfying join condition in the
common column are displayed.
SELECT columns
FROM tablename_1
INNER JOIN tablename_2 ON
tablename_1.column join_operator tablename_2.column;
[1]. Inner Join
Table 1 Table 2
Common Attribute

27. [2]. Equi Join
• Same as INNER Join. However,
– Only the equality operator is used to specify the
join condition
SELECT columns
FROM table1
INNER JOIN table2
ON table1.column = table2.column

28. [3]. Outer Join
• When OUTER join is applied, the result set
containing all the rows from one table and
matching rows from other table.
SELECT columns
FROM tablename_1 [LEFT | RIGHT | FULL] OUTER JOIN
tablename_2
ON tablename_1.column join_operator tablename_2.column
[WHERE search_condition]

29. OUTER join displays NULL for the column where
it doesn’t find any matching record.
NOTE

30. [3]. TYPES of Outer Join
• LEFT Outer Join
– All the rows from the table specified on left side of
the LEFT OUTER JOIN keyword (Table 1) and
matching from table specified on right side (Table 2)
Table 1 Table 2Table 2Table 1
• RIGHT Outer Join
– All the rows from the table specified on right side of
the RIGHT OUTER JOIN keyword (Table 2) and
matching from table specified on left side (Table 1)
• FULL Outer Join
– Combination of LEFT and RIGHT outer join.
– Result set contain all the matching and non
matching rows from both the table.
Table 2Table 1

31. What is the difference between
• A LEFT OUTER JOIN B is equivalent to B RIGHT
OUTER JOIN A, with the columns in a different
order.

32. [4]. CROSS Join
• A CROSS JOIN is also known as Cartesian
Product.
• It joins each row of one table with each row of
the other table.
• Unlike other JOIN operators, it does not let
you specify a join clause.

33. GROUPING DATA

34. Grouping Related Data
• GROUP BY clause of SELECT statement is used to
summarizes the result set into groups.
• HAVING clause further restricts or eliminates
groups that do not match the condition.
SELECT column_list
FROM table_name
WHERE condition
[GROUP BY expression [ROLLUP | CUBE]
[GROUPING SET]
[HAVING search_condition]

35. Grouping Related Data
• GROUP BY clause
– collects data the match the condition,
– summarizes it using aggregated function
– produce a single value for each group.
• GROUP BY clause can be applied on multiple
fields.

36. Grouping Related Data
• GROUPING SETS clause is used to combine the
result generated by multiple GROUP BY clause
into a single result set.
SELECT column_list
FROM table_name
WHERE condition
[GROUP BY GROUPING SETS ( (columnname),...]
[HAVING search_condition]

37. Grouping Related Data
• ROLL UP clause ROLLUP calculates
aggregations at increasing levels of
aggregation, from the most detailed up to a
grand total.
• ROLLUP creates subtotals at n+1 levels, where
n is the number of grouping columns

38. Grouping Related Data - ROLLUP
– ROLLUP (year, month, day), it means stepping
back to determine
(year, month, day)
(year, month)
(year)
()
SELECT column_list
FROM table_name
WHERE condition
[GROUP BY ROLLUP( (columnname),
columnname2, ...]
[HAVING search_condition]

39. Grouping Related Data
• CUBE clause calculate subtotals for all possible
combinations of a group of dimensions.
• It also calculates a grand total.
• If there are n columns specified for a CUBE,
there will be 2n combinations of subtotals
returned

40. Grouping Related Data
• CUBE (year, month, day), creates a grouping for
every possible combination of columns
(year, month, day)
(year, month)
(year, day)
(year)
(month, day)
(month)
(day)
()
SELECT column_list
FROM table_name
WHERE condition
[GROUP BY CUBE( (columnname), columnname2,
...]
[HAVING search_condition]

41. USING SUBQUERIES

42. What is Subquery?
• Subquery is a query statement appears inside
another SQL statement.
• Subqueries are also called nested queries.
– Nested inside WHERE and HAVING clause of
SELECT, INSERT, DELETE and UPDATE statements.
• We can nest up to 255 levels of subqueries in
the WHERE clause.

43. How Subquery Works?
• Query that represents the parent query is
called the outer query.
• Query that represent the subquery is called
the inner query.
– Inner Query executes first.
– Inner Query returns values that are used by the
outer query.
– Inner Query can return one or more values

44. Subquery Rules and Guidelines
• A subquery must be enclosed in parentheses ().
• A subquery must be placed on the right side of the
comparison operator.
• If the WHERE clause of an outer query includes a
column name, it must be join-compatible with the
column in the inner query select list.
• Use single-row operators with single-row subqueries.

45. Subquery Rules and Guidelines
• ORDER BY can only be specified when TOP is also
specified.
• A view created by using a subquery cannot be
updated.
• The SELECT list cannot include any references to
values that evaluatse to a BLOB, ARRAY, CLOB, or
NCLOB.

46. Using IN keyword with Subquery
• When subquery returns more than one value,
IN keyword is used.
SELECT column1, column2, .....columnn
FROM tablename
WHERE column [NOT] IN
( SELECT column FROM table_name
[WHERE search_condition ] )

47. Using EXISTS keyword with Subquery
• EXISTS keyword is used to check if a set of
records exists or not.
• EXISTS keyword always return TRUE or FALSE
value.
SELECT column1, column2, .....columnn
FROM tablename
WHERE EXISTS
( SELECT column FROM table_name
[WHERE search_condition ] )

48. Subquery Rules and Guidelines
• EXISTS keyword is not preceded by any column
name, constant or any expression.
• If EXISTS keyword is used, inner query must contain
(*) in the SELECT statement instead of single column
name.

49. Subquery - Using Modified Comparison
Operator
• ANY and ALL keyword can be used with
comparison operator.
– ALL keyword
• Returns TRUE if all the values returned by inner query
satisfy comparison operator.
– ANY keyword
• Returns TRUE if any value returned by inner query
satisfies comparison operator.

50. Types of Subqueries
• Single row subquery
– Returns zero or one row.
• Multiple row subquery
– Returns one or more rows.
• Multiple column subqueries
– Returns one or more columns.

51. Types of Subqueries
• Correlated subqueries :

52. SET OPERATIONS

53. Union and UNION ALL Operator
• Combines the results of two or more queries
into a single result set.
• Difference between UNION and UNION ALL
– UNION operator eliminates duplicate selected
rows.
– The UNION ALL operator does not eliminate
duplicate selected rows.

54. INTERSECT Operator
• Combines the results of two or more queries
and returns only common rows returned by
both queries.

55. Minus Operator
• Combines the results of two queries and
returns only unique rows present in first query
but not by the second.

56. Example: Set Operation
Consider two sets
A = {101, 103, 104, 107, 110, 112} and
B= {103, 104, 106, 110}
Find A union B , A intersect B, A minus B
– A UNION B = { 101, 103, 104, 106, 107, 110, 112}
– A INTERSECT B = { 103, 104, 110}
– A MINUS B = { 101, 107, 112}

57. Restrictions on the Set Operators
• The number and sequence of the columns must be
same in all the queries.
• The datatypes of the columns in all the queries must be
compatible.
• The set operators are not valid on columns of type
LONG, BLOB, CLOB, BFILE, VARRAY, or nested table.
• You cannot specify the ORDER BY clause in the
subquery of these operators.