约束有两种类型：表级约束和列约束。

Constraints come in two types: table-level constraints and column constraints.

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这意味着表必须有一个或多个列级或表级约束。

This implies that the table must have one or more columns or table-level constraints.

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在这个语法示例中，必须定义一个新列或者定义一个表级约束。

In this syntax example, you must either define a new column or define a new table-level constraint.

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在这个语法示例中，必须定义一个新列或者定义一个表级约束。

In this syntax example, you must either define a new column or define a new table-level constraint.

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