如何实现仅在第一个WHERE条件不满足时执行第二个WHERE条件？

首先得先修正你原查询里的一个语法错误：AND INNER JOIN这里多了个多余的AND，得删掉，不然会直接触发语法报错。

回到你的核心需求：仅当condition1不满足时，才去判断condition2到condition6这些条件，换句话说，最终的筛选逻辑应该是：

• 要么满足condition1，
• 要么不满足condition1，但满足condition2到condition6中的任意一个

对应的SQL写法可以这样调整WHERE子句：

SELECT B.col1, B.col2, B.col3 
FROM (SELECT firstname, lastname FROM employee) A 
INNER JOIN (SELECT col1, col2, col3 FROM office) B 
  ON TRIM(A.firstname) = TRIM(B.col1) 
INNER JOIN (SELECT col4, col5, col6 FROM school) C 
  ON TRIM(A.firstname) = TRIM(C.col4) 
WHERE condition1 
   OR (NOT condition1 AND (condition2 OR condition3 OR condition4 OR condition5 OR condition6));

这个写法利用了SQL的逻辑短路特性：当condition1满足时，后面的(NOT condition1 AND ...)部分会直接跳过，不会再去判断后续条件，刚好实现你要的“仅在第一个条件不满足时才执行第二个及后续条件”的效果。

如果你的需求是完全排除同时满足condition1和后续条件的行（也就是只保留“仅满足condition1”或者“不满足condition1但满足后续任意条件”的行），那逻辑就要改成这样：

SELECT B.col1, B.col2, B.col3 
FROM (SELECT firstname, lastname FROM employee) A 
INNER JOIN (SELECT col1, col2, col3 FROM office) B 
  ON TRIM(A.firstname) = TRIM(B.col1) 
INNER JOIN (SELECT col4, col5, col6 FROM school) C 
  ON TRIM(A.firstname) = TRIM(C.col4) 
WHERE (condition1 AND NOT (condition2 OR condition3 OR condition4 OR condition5 OR condition6))
   OR (NOT condition1 AND (condition2 OR condition3 OR condition4 OR condition5 OR condition6));

你可以根据自己的实际业务场景选择对应的写法~

内容的提问来源于stack exchange，提问作者Kiran Kumar