The document discusses SQL commands for updating tables, deleting rows from tables, adding and modifying columns in tables, removing tables and views, and using aggregate functions and clauses. It provides syntax examples for the UPDATE, DELETE, ALTER TABLE, DROP TABLE, CREATE VIEW, DROP VIEW, and aggregate function/GROUP BY/HAVING clauses.

1. UPDATE - UPDATING A TABLE
• Changes values in a table
Syntax:
UPDATE <table name>/<view name>
SET <column name> = <new value>
[,<column name> = <new value>...]
[<WHERE clause>];
• The WHERE clause specifies the rows to be UPDATEd
• Omitting this clause UPDATEs all rows in the table.
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2. Ex:
UPDATE EMP
SET salary = salary +1000
WHERE Job = ‘Analyst’ ;
UPDATE EMP
SET salary = salary +1000,
comm = 5000
WHERE Job = ‘SALESMAN’ ;
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3. DELETE - DELETING ROWS FROM A TABLE
•Removes one or more rows from a table.
DELETE FROM <table name> [<alias name>]
[<WHERE clause>];
• The WHERE clause specifies rows to be deleted.
• If the WHERE clause is not included, all rows will be
deleted.
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4. DELETE FROM Employee WHERE name =
'Mihir';
DELETE * FROM Employee;
DELETE FROM Employee WHERE name NOT
IN (‘Tony’, ‘Tom’);
DELETE FROM Employee WHERE salary <
10000;
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5. ALTER TABLE - ADDING ATTRIBUTES TO A
TABLE
•Adds new columns to a table.
ALTER TABLE <table name>
ADD (<column name> <data type>
[,<column name> <data type>...]);
Ex: ALTER TABLE staff
ADD (phone CHAR(13));
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6. ALTER TABLE staff
drop column phone;
ALTER TABLE staff
modify name varchar2(40);
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7. DROP TABLE – REMOVING A TABLE
Removes specified table from the active database.
DROP TABLE <table name>;
When you DROP a table, all indexes, synonyms, and
views associated with it are DROPped.
Ex: DROP TABLE emp;
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8. CREATE VIEW – CREATING A VIEW
Defines a view that combines data from one or
more tables/views.
A column list must be specified if any of the
columns in the SELECT are calculated columns or
expressions, otherwise view columns inherit default
names from the base table(s)/view(s).
CREATE VIEW <view name> [(<column name>,
<column name>..)]
AS <SELECT command> [WITH CHECK
OPTION];
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9. Ex:
CREATE VIEW emp AS SELECT * FROM
Employee
WHERE dept = 'SOFTWARE';
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10. DROP VIEW – REMOVING A VIEW
Removes specified view from the active database.
DROP VIEW <view name>;
When a view is DROPped, all other views and
synonyms based on it are dropped automatically.
When a table is dropped, all views based on it are also
dropped.
Ex: DROP VIEW empview;
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11. Aggregate functions
Aggregate functions work with a group of values and
reduce them to a single value.
COUNT
• counts rows/records
• * can be used instead of ALL
COUNT ({*/[DISTINCT] <column name>})
• Used in SELECT or HAVING clause to count the
number of rows returned by an SQL command
• DISTINCT omits any repeated values
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12. •If used in the SELECT clause, all other columns
SELECTed must also be SQL aggregate functions or
columns specified in a GROUP BY clause
Examples
SELECT COUNT (*) FROM staff WHERE salary >
15500;
SELECT COUNT (DISTINCT name) FROM Employee;
SELECT COUNT (*) FROM Employee;
SELECT COUNT(ALL desig) from Employee where
salary >15500;
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13. MAX and MIN
• Used in SELECT or HAVING clauses
• MAX() function returns the highest value in the specified
column or column expression
• MIN() returns the lowest value
• If used in the SELECT clause, all other columns selected
must also be SQL aggregate functions or columns specified
in a GROUP BY clause.
{MAX/MIN} ([ALL/DISTINCT] <column name>)
SELECT MAX (salary), MIN (salary) FROM Emp;
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14. SUM
• Used in the SELECT or HAVING clauses to find the
sum of values for the specified column.
• ALL is the default.
• DISTINCT omits any repeated values.
• If used in the SELECT clause, all other columns
SELECTed must also be SQL aggregate functions or
columns specified in a GROUP BY clause.
SUM ([ALL/DISTINCT] <column name>)
SELECT SUM(salary) from Emp;
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15. AVG
Used in the SELECT or HAVING clause to find the
average value for the specified column or column
expression.
ALL is the default.
DISTINCT omits any repeated values.
If used in the SELECT clause, all other columns
SELECTed must also be SQL aggregate functions or
columns specified in a GROUP BY clause.
AVG ([ALL/DISTINCT] <column name>)
SELECT AVG (Height) FROM Student;
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16. AGGREGATE CLAUSES : GROUP BY AND
HAVING
GROUP BY clause
• Is used to divide the rows in a table into smaller groups
• Grouping can be done by a column name, or with
aggregate function
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17. GROUP BY <column name>[,<column name>...]
• Group functions (AVG, MAX, MIN, SUM, COUNT)
can be used with group by clause to return summary
information for each group
• Any non-aggregate function columns in a SELECT
clause that includes aggregate functions must be specified
in a GROUP BY clause
• You cannot GROUP BY columns of type LOGICAL
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18. • Groups rows together that have duplicate values for the
specified column
• SQL aggregate functions (AVG, MAX, MIN, SUM, or
COUNT) in a SELECT clause operate on each group
• Any non-aggregate function columns in a SELECT
clause that includes aggregate functions must be specified
in a GROUP BY clause
• You cannot GROUP BY columns of type LOGICAL
• WHERE clause can be used to exclude rows before
forming groups
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19. SELECT Class, COUNT(Sname) FROM Student GROUP
BY Class;
SELECT Dept, COUNT(ename) FROM Emp GROUP
BY dept;
SELECT Class, AVG(Height) FROM Student GROUP
BY Class;
SELECT Dept, MAX(salary) FROM Emp WHERE DOJ
> ’01-Jan-2005’ GROUP BY dept;
SELECT Class, Sec, COUNT(*) FROM Student GROUP
BY Class, Sec;
(Group all students by class, then within each class group
by sec)
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20. HAVING clause
• Used to restrict groups returned from GROUP BY
clause
• places condition on groups
• can include aggregate functions
HAVING [NOT]<search condition>
• In a query using GROUP BY and HAVING clause,
the rows are first grouped, group functions are applied
and then only those groups matching HAVING clause
are displayed
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21. SELECT dept, MAX(salary) FROM Emp
GROUP BY dept
HAVING COUNT(*) > 10;
SELECT job_code,avg(salary), sum(salary)
from Emp
GROUP BY job_code
HAVING job_code=3;
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