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CONSTRAINTS\u003c/code\u003e强制在事务中的特定点执行约束检查。\u003c/p\u003e\u003cp\u003e当前，只有\u003ccode\u003eUNIQUE\u003c/code\u003e、\u003ccode\u003ePRIMARY KEY\u003c/code\u003e、\u003ccode\u003eREFERENCES\u003c/code\u003e（外键）以及\u003ccode\u003eEXCLUDE\u003c/code\u003e 约束受到这个设置的影响。\u003ccode\u003eNOT NULL\u003c/code\u003e和\u003ccode\u003eCHECK\u003c/code\u003e约束总是在一行被插入或修改时立即检查（\u003cspan\u003e\u003cem\u003e不是\u003c/em\u003e\u003c/span\u003e在语句结束时）。未声明为\u003ccode\u003eDEFERRABLE\u003c/code\u003e的唯一约束和排他约束也会立即检查。\u003c/p\u003e\u003cp\u003e被声明为\u003cspan\u003e“\u003cspan\u003e约束触发器\u003c/span\u003e”\u003c/span\u003e的触发器，其引发也受此设置控制 — 它们会在相关约束应当被检查的同时引发。\u003c/p\u003e\u003c/section\u003e\u003csection\u003e\u003ch2\u003e注解\u003c/h2\u003e\u003cp\u003e因为\u003cspan\u003ePostgreSQL\u003c/span\u003e并不要求约束名称在同一模式内唯一（只要求在每个表内唯一），所以指定的约束名称有可能匹配到多个约束。在这种情况下，\u003ccode\u003eSET 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