Constraints Supports, primary, foreign, unique, not null constraint.

约束支持主键、外键、惟一和非空约束。

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If a NOT NULL constraint is specified, then the column must have a default value other than NULL.

如果规定一个不允许有空值是一个约束，那么字段必须有一个不同于空值的默认值。

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So in the example above, the NOT NULL constraint would get violated, and the INSERT statement would error out.

因此，在上面的示例中，会违反NOT NULL约束，INSERT语句会出错。

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In Oracle 10g, if there is a BEFORE INSERT TRIGGER and a NOT NULL constraint on a table, then the BEFORE TRIGGER is executed first, and then the constraint check is performed.

在Oracle10g中，如果表上同时存在BEFORE INSERT触发器和NOT NULL约束，那么先执行BEFORE触发器，然后执行约束检查。

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For example, if a before trigger supplies value to a NOT NULL column, then the before trigger is executed first and a value is supplied to the column so that the NOT NULL constraint isn't violated.

例如，如果一个BEFORE触发器给一个NOT null列提供值，那么先执行BEFORE触发器，给列提供值，所以不会违反NOT NULL约束。

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The itemNumber column provides a unique identity for each item (or row) and has an attached column-level constraint that enforces a valid value to always be supplied (NOT NULL).

itemNumber列提供了每个商品（或列）的惟一标识，它上面还有列级约束，强制要求提供正确的值（NOT NULL）。

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A workaround to this is to supply a default value to the not NULL column whose value comes from a BEFORE INSERT TRIGGER, so that the constraint is not violated.

一种解决方法是给从BEFORE INSERT触发器取得值的NOT null列提供默认值，这样就不会违反约束。

youdao

A workaround to this is to supply a default value to the not NULL column whose value comes from a BEFORE INSERT TRIGGER, so that the constraint is not violated.

一种解决方法是给从BEFORE INSERT触发器取得值的NOT null列提供默认值，这样就不会违反约束。

youdao