Difference between revisions of "UNIQUE Column Constraint"
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==Purpose== | ==Purpose== | ||
Column constraint to define a candidate index for a table | Column constraint to define a candidate index for a table | ||
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==Syntax== | ==Syntax== | ||
UNIQUE [COLLATE <cCollateSequence>] | UNIQUE [COLLATE <cCollateSequence>] | ||
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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 optional COLLATE <cCollateSequence> clause is included for Visual FoxPro language compatibility only. | The optional COLLATE <cCollateSequence> clause is included for Visual FoxPro language compatibility only. | ||
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==Example== | ==Example== | ||
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acc_name char(20) UNIQUE) | acc_name char(20) UNIQUE) | ||
</code> | </code> | ||
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==Products== | ==Products== | ||
| − | + | Lianja, Lianja Server | |
[[Category:Documentation]] | [[Category:Documentation]] | ||
[[Category:SQL]] | [[Category:SQL]] | ||
Latest revision as of 11:23, 11 December 2012
Purpose
Column constraint to define a candidate index for a table
Syntax
UNIQUE [COLLATE <cCollateSequence>]
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 UNIQUE column constraint is used to define the column as a candidate index for the table. A unique tag index is built on the specified column; it is given the same name as the column. More than one column can be defined as a candidate index for the table.
The optional COLLATE <cCollateSequence> clause is included for Visual FoxPro language compatibility only.
Example
CREATE TABLE newcust; (acc_ref char(5) default strzero(seqno(),5) UNIQUE,; acc_name char(20) UNIQUE)
Products
Lianja, Lianja Server
