如果不存在则添加约束

发布于 2025-01-14 06:24:31 字数 216 浏览 4 评论 0原文

我想将“检查”约束添加到某个表，但首先我必须检查该约束是否存在。我的 SQL 脚本中有一些错误。正确的做法是什么？

   ALTER TABLE public.ELEMENTS ADD CONSTRAINT IF NOT EXISTS elements_check CHECK ((t1_id IS NOT NULL) OR (t2_id IS NOT NULL));

原文

I want to add the 'check' constraint to some table, but firstly I have to check if that constraint exists. I have some error in my SQL script. What is the corret way to do it ?

   ALTER TABLE public.ELEMENTS ADD CONSTRAINT IF NOT EXISTS elements_check CHECK ((t1_id IS NOT NULL) OR (t2_id IS NOT NULL));

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灰色世界里的红玫瑰 2025-01-21 06:24:32

我使用此语句来检查 SQL Server 中是否存在主键。

SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'PrimaryKeyName') AND type in (N'PK') AND parent_object_id = OBJECT_ID(N'TableName')

I use this statement to check wherever a Primary Key exists or not in SQL Server.

SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'PrimaryKeyName') AND type in (N'PK') AND parent_object_id = OBJECT_ID(N'TableName')

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装迷糊 2025-01-21 06:24:31

根据手册：

ALTER TABLE ... DROP CONSTRAINT IF EXISTS 确实存在
ALTER TABLE ... ADD CONSTRAINT IF NOT EXISTS 不存在，

因此您必须在 2. 之前执行 1. ：

ALTER TABLE public.ELEMENTS DROP CONSTRAINT IF EXISTS elements_check ;

ALTER TABLE public.ELEMENTS ADD CONSTRAINT elements_check CHECK ((t1_id IS NOT NULL) OR (t2_id IS NOT NULL));

According to the manual :

ALTER TABLE ... DROP CONSTRAINT IF EXISTS do exist
ALTER TABLE ... ADD CONSTRAINT IF NOT EXISTS doesn't exist

so you have to execute 1. before 2. :

ALTER TABLE public.ELEMENTS DROP CONSTRAINT IF EXISTS elements_check ;

ALTER TABLE public.ELEMENTS ADD CONSTRAINT elements_check CHECK ((t1_id IS NOT NULL) OR (t2_id IS NOT NULL));

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