Difference between revisions of "SET NULL"
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==Description== | ==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. | 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. | ||
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==Example== | ==Example== | ||
Revision as of 06:55, 10 February 2012
Contents
Purpose
To determine NULL value support
Syntax
SET NULL ON | OFF
See Also
ALTER TABLE, CREATE TABLE, EMPTY(), INSERT, ISBLANK(), ISNULL(), NVL(), 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.
Example
set sql 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...
