SQL constraints are used to specify rules for data in a table.
Constraints can be specified when the table is created with the CREATE TABLE statement, or after the table is created with the ALTER TABLE statement.
Syntax
CREATE TABLE table_name (
column1 datatype constraint,
column2 datatype constraint,
column3 datatype constraint,
....
);
column1 datatype constraint,
column2 datatype constraint,
column3 datatype constraint,
....
);
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