Revision as of 17:13, 10 March 2009

SET NULL

Class

SQL Applications

Purpose

To determine NULL value support

Syntax

SET NULL ON | OFF

See Also

ALTER TABLE, CREATE TABLE, INSERT, EMPTY(), ISBLANK(), ISNULL(), SET NULLDISPLAY

Description

The SET NULL ON | OFF command is used to determine whether columns in a table support NULL values. With SET NULL ON, table columns will support NULL values by default. INSERT will insert a NULL into any column that does not have a value specified. With SET NULL off, NULL values are not supported by default. INSERT will insert a NULL into any column that does not have a value specified.. This default can be overridden by specifying the NULL or NOT NULL column constraint on an individual column.

SET NULL is OFF by default.

Example

set sqldialect to vfp
set null on
CREATE TABLE nullon (firstname c(20), lastname c(20))
INSERT INTO nullon (lastname) VALUES ("Smith")
? [SET NULL ON]
? [ISNULL() ], isnull(firstname)
? [EMPTY() ], empty(firstname)
wait
SET NULL ON
ISNULL()  .T.
EMPTY()  .F.
Press any key to continue...

set null off
CREATE TABLE nulloff (firstname c(20), lastname c(20))
INSERT INTO nulloff (lastname) VALUES ("Smith")
? [SET NULL OFF]
? [ISNULL() ], isnull(firstname)
? [EMPTY() ], empty(firstname)
wait
SET NULL OFF
ISNULL()  .F.
EMPTY()  .T.
Press any key to continue...

 
set null off
CREATE TABLE nulloff2 (firstname c(20) NULL, lastname c(20))
INSERT INTO nulloff2 (firstname,lastname) VALUES (NULL,"Smith")
? [SET NULL OFF, NULL Column Constraint]
? [ISNULL() ], isnull(firstname)
? [EMPTY() ], empty(firstname)
wait
SET NULL OFF, NULL Column Constraint
ISNULL()  .T.
EMPTY()  .F.
Press any key to continue...

Products

Recital Database Server, Recital Mirage Server, Recital Terminal Developer