Difference between revisions of "DEFAULT Column Constraint"
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==Purpose== | ==Purpose== | ||
Column constraint to set a default value for the specified column | Column constraint to set a default value for the specified column | ||
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==Syntax== | ==Syntax== | ||
DEFAULT <expr> | DEFAULT <expr> | ||
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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 DEFAULT column constraint is used to set a default value for the specified column. The <expr> must evaluate to the same data type as the target column. The column's value can subsequently be updated. | The DEFAULT column constraint is used to set a default value for the specified column. The <expr> must evaluate to the same data type as the target column. The column's value can subsequently be updated. | ||
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==Example== | ==Example== | ||
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[[Category:Documentation]] | [[Category:Documentation]] | ||
[[Category:SQL]] | [[Category:SQL]] | ||
Revision as of 07:58, 7 December 2012
Contents
Purpose
Column constraint to set a default value for the specified column
Syntax
DEFAULT <expr>
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 DEFAULT column constraint is used to set a default value for the specified column. The <expr> must evaluate to the same data type as the target column. The column's value can subsequently be updated.
Example
ALTER TABLE customer; ADD COLUMN dateref DATE DEFAULT date()
