ISNULL – SQL Server Syntax Example: ISNULL – T-SQL Example

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ISNULL – SQL Server Syntax Example: ISNULL – T-SQL Example

Purpose: – Illustrates the SQL Server syntax for the ISNULL.

SYNTAX:

SELECT [ ALL | DISTINCT ]
[TOP ( expression ) [PERCENT] [ WITH TIES ] ]
column_list, ISNULL(check_expression, replacement_value)
[ INTO new_table ]
[ FROM { table_source } [ ,...n ] ]
[ WHERE search_condition ]
[ GROUP BY ]
[ HAVING search_condition ]
[ ORDER BY order_expression [ ASC | DESC ]

PURPOSE:
IS NULL returns true or false indicating whether value is NULL.

Code Sample for ISNULL:

 T-SQL | 
 copy code |
?
 
 
/* ISNULL example from http://idealprogrammer.com 
 PURPOSE: ISNULL is used in SELECT clause to replace NULL values with a default
           value. Do not use ISNULL in WHERE clause to find NULL - use IS NULL 
           instead.
 
 SYNTAX: ISNULL(check_expression, replacement_value)
 
 SELECT [ ALL | DISTINCT ] 
			[TOP ( expression ) [PERCENT] [ WITH TIES ] ] 
			 column_list, ISNULL(check_expression, replacement_value)  
			[ INTO new_table ] 
			[ FROM { table_source } [ ,...n ] ] 
			[ WHERE test_expression IS [NOT] NULL ] 
			[ GROUP BY ] 
			[ HAVING  search_condition  ] 
			[ ORDER BY  order_expression [ ASC | DESC ] ] 
*/
 
 
CREATE TABLE people(
     ID          int,
     firstname   varchar (20),
     lastname    varchar (20),
     statecode   varchar (2),
     alive       bit,
     height      int )
 GO
 
 
 
 
 
 
 INSERT INTO people (ID, firstname, lastname, statecode, alive) -- height is NULL
 VALUES (1,  'Paul', 'Revere', 'AL', 0)
 GO
 
 INSERT INTO people (ID, firstname, lastname, statecode, alive, height) 
 VALUES (2,  'John', 'Lennon', 'NY', 0, 69)
 GO
 
 INSERT INTO people (ID, firstname, lastname, statecode, alive, height)
 VALUES (3,  'Steve', 'Martin', 'NY', 1, 75)
 GO
 
 INSERT INTO people (ID, firstname, lastname, statecode, alive, height)
 VALUES (4,  'George', 'Washington', 'VA', 0, 75)
 GO
 
 -- Select entire table
 SELECT 'Entire Table', * FROM people
 
 -- 1. Using ISNULL to replace column values when null
 SELECT 'Example #1' as Example, statecode, ISNULL(height,79)  
  FROM people  
 
 GO
 
 -- 2. Using ISNULL with AVG to replace all NULL heights with 350
 SELECT 'Example #2' as Example, AVG(ISNULL(height,350)) As Avg_Height 
  FROM people  
 
 GO
 
 
 
 
 
 DROP TABLE people;
 
 GO
 
 
 
 
 
 
 
 
 
 

Sample Output for ISNULL Example

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