Sqlite和Mysql和SqlServer中insert … select … where not exist的用法
下面介绍Mysql和Sqlite和Sqlserver中，根据select的条件判断是否插入。例如：
一、Mysql中：
INSERT INTO books (name) SELECT 'SongXingzhu' FROM dual WHERE NOT EXISTS (SELECT id FROM books WHERE id = 1)
二、Sqlite中：
由于Sqlite中没有临时表：dual
所以，需要这样写
INSERT INTO books (name) SELECT 'Songxingzhu' WHERE NOT EXISTS (SELECT id FROM books WHERE id = 1)
三、Sqlserver中：
SqlServer中需要另一种写法：
IF NOT EXISTS (SELECT id FROM books WHERE id = 1) INSERT INTO books (name) SELECT 'Songxingzhu'
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