Keyon's PagesBlog (gitee.io)

查询

LIMIT

限制查询数量

ORDER BY 排序

指定排序方向

为了进行降序排序，必须指定DESC关键字

单列逆序

SELECT prod_id, prod_price
FROM products
ORDER BY prod_price DESC;

多列排序

一个DESC只作用一个列（DESC前面那列），如果多列，必须对每列都指定DESC

SELECT prod_id, prod_price, prod_name
FROM products
ORDER BY prod_price DESC, prod_name;

ORDER BY+LIMIT查询最值

SELECT prod_price
FROM products
ORDER BY prod_price DESC
LIMIT 1;

WHERE

IS NULL子句

检查具有NULL值的列。

SELECT prod_name
FROM products
WHERE prod_price IS NULL;

WHERE+AND\OR