Difference between revisions of "NULL Column Constraint"
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==Purpose== | ==Purpose== | ||
Column constraint to allow NULL values | Column constraint to allow NULL values | ||
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==Syntax== | ==Syntax== | ||
NULL | NULL | ||
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==See Also== | ==See Also== | ||
[[ALTER TABLE]], [[SQL Constraints|CONSTRAINTS]], [[CREATE TABLE]] | [[ALTER TABLE]], [[SQL Constraints|CONSTRAINTS]], [[CREATE TABLE]] | ||
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==Description== | ==Description== | ||
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The NULL column constraint is used to specify that the column can contain NULL values. The NOT NULL column constraint can be used to disallow NULL values. | The NULL column constraint is used to specify that the column can contain NULL values. The NOT NULL column constraint can be used to disallow NULL values. | ||
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==Example== | ==Example== | ||
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</code> | </code> | ||
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[[Category:Documentation]] | [[Category:Documentation]] | ||
[[Category:SQL]] | [[Category:SQL]] | ||
Revision as of 08:11, 7 December 2012
Contents
Purpose
Column constraint to allow NULL values
Syntax
NULL
See Also
ALTER TABLE, CONSTRAINTS, CREATE TABLE
Description
A constraint is used to define rules that help to provide data integrity. Column constraints are specific to the column name specified. You must have ALTER privilege on the table. The table will be locked for EXCLUSIVE use during the operation.
The NULL column constraint is used to specify that the column can contain NULL values. The NOT NULL column constraint can be used to disallow NULL values.
Example
ALTER TABLE customer; ADD COLUMN custref CHAR(5) NULL ALTER TABLE customer; ALTER COLUMN custref NOT NULL
