SQL Constraints: Difference between revisions
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=Primary Key Constraint= | =Primary Key Constraint= | ||
{{Internal|Relational_Databases#Primary_Key|Primary Key}} | |||
<syntaxhighlight lang='sql'> | <syntaxhighlight lang='sql'> | ||
CREATE TABLE ... | CREATE TABLE ... | ||
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); | ); | ||
</syntaxhighlight> | </syntaxhighlight> | ||
=Foreign Key Constraint= | =Foreign Key Constraint= | ||
<syntaxhighlight lang='sql'> | <syntaxhighlight lang='sql'> | ||
Revision as of 00:04, 23 May 2024
Internal
Overview
NOT NULL Constraint
CREATE TABLE ...
( ...
somecolumn varchar(30) NOT NULL,
...
);
Also see:
Primary Key Constraint
CREATE TABLE ...
( ...
CONSTRAINT pk_someconstraint PRIMARY KEY (somecolumn)
);
Foreign Key Constraint
CREATE TABLE ...
( ...
CONSTRAINT fk_someconstraint FOREIGN KEY (somecolumn)
);
Check Constraint
CREATE TABLE ...
( ...
eye_color CHAR(2) CHECK (eye_color IN ('BR', 'BL', 'GR')),
...
);