相关疑难解决方法(0)

每当我需要检查表中某行是否存在时，我总是倾向于编写如下条件：

SELECT a, b, c
  FROM a_table
 WHERE EXISTS
       (SELECT *  -- This is what I normally write
          FROM another_table
         WHERE another_table.b = a_table.b
       )

还有一些人这样写：

SELECT a, b, c
  FROM a_table
 WHERE EXISTS
       (SELECT 1   --- This nice '1' is what I have seen other people use
          FROM another_table
         WHERE another_table.b = a_table.b
       )

当条件NOT EXISTS不是EXISTS: 在某些情况下，我可能会用 aLEFT JOIN和一个额外的条件（有时称为antijoin）来编写它：

SELECT a, b, c
  FROM a_table
       LEFT JOIN another_table ON another_table.b = …