AND

OR

HAVING

NOT

CHAR_LENGTH('SQL') 和 LENGTH('SQL') 的结果一定相同

LENGTH(NULL) 返回 NULL

LENGTH('中文') 在 Unicode 字符集中返回值可能大于 2

CHAR_LENGTH 统计的是字符数，而非字节数

select a, min(b) from table group by a, c不会报错

select a, b, c from table group by a, b, c, d不会报错

select a, b, c from table group by a, c, d不会报错

select a, b, c from table group by a, c不会报错

子查询必须始终用括号()括起来

 子查询是嵌套在另一个查询（主查询）内部的查询

子查询可以出现在SELECT、FROM、WHERE、HAVING子句中

子查询的执行总是独立于主查询，先于主查询完成

DENSE_RANK() OVER (PARTITION BY employee_id, MONTH(sale_date) ORDER BY sale_amount DESC)

RANK() OVER (PARTITION BY employee_id, MONTH(sale_date) ORDER BY sale_amount DESC)

ROW_NUMBER() OVER (PARTITION BY employee_id, MONTH(sale_date) ORDER BY sale_amount DESC)

DENSE_RANK() OVER (PARTITION BY MONTH(sale_date) ORDER BY sale_amount DESC)

FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY → LIMIT

SELECT → FROM → WHERE → GROUP BY → HAVING → ORDER BY → LIMIT

FROM → WHERE → SELECT → GROUP BY → HAVING → ORDER BY → LIMIT

FROM → ON → JOIN → WHERE → GROUP BY → HAVING → SELECT → ORDER BY → LIMIT