Along with the basic table structure (number, name and data type of columns, name and location of the table), the CREATE TABLE statement and ALTER TABLE statement can specify many different table attributes that allow control over data integrity. Constraints allow you to place restrictions on the values that can appear in a column, or on the relationship between values in different columns. Constraints can be either table-wide constraints, or can apply to individual columns.
This section describes how to use constraints to help ensure the accuracy of data in the table.
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