PostgreSql 、Mysql和Sqlite通过A表更新B表

PostgreSql 与mysql 有很大的不同，表表更新就是一个例子

1. 下面是PostgreSql 的通过A表更新B表

正确写法

update mesh set plan_id=p.id from plan p where mesh.project_id='201028085428118000' and mesh.project_id=p.project_id;

这里面有2张表，一张是mesh表，另一张是plan 表 切记需要更新的表（mesh）不能使用别名否则会报错，具体原因我也不清楚

2. 再来一个mysql的表表更新

update mesh a,plan b  set  a.plan_id=b.plan_id where  a.project_id=b.project_id and a.project_id='201028085428118000'

3.Sqlite中表表更新的写法

UPDATE table_a
SET
      table_a.column_a_1 = (SELECT table_b.column_b_1 
                            FROM table_b
                            WHERE table_b.user_name = table_a.user_name )
    , table_a.column_a_2 = (SELECT table_b.column_b_2
                            FROM table_b
                            WHERE table_b.user_name = table_a.user_name )
WHERE
    EXISTS (
        SELECT *
        FROM table_b
        WHERE table_b.user_name = table_a.user_name
    )