操作符
用来联结或改变WEHERE子句中的子句的关键字,也称为逻辑操作符。
AND操作符(同时满足条件)
一个AND两个条件,如果有多个条件,那么两个条件之间加一个AND
SELECT prod_id,prod_price,prod_name
FROM products
WHERE vend_id = 'DLL01' AND prod_price<=4
ORDER BY prod_name
OR操作符(第1个条件满足,不管第二个,满不满足都将被检索出)
SELECT prod_id,prod_price,prod_name
FROM products
WHERE vend_id = 'DLL01' OR vend_id = 'DLL02'
求值顺序
猜猜区别
SELECT vend_id,prod_price,prod_name
FROM products
WHERE vend_id = 'DLL01' OR vend_id = 'BRS01' AND prod_price >= 10
SELECT vend_id,prod_price,prod_name
FROM products
WHERE vend_id = 'DLL01' OR (vend_id = 'BRS01' AND prod_price >= 10)
SELECT vend_id,prod_price,prod_name
FROM products
WHERE (vend_id = 'DLL01' OR vend_id = 'BRS01') AND prod_price >= 10
前两个一样,AND的优先级比较高
最后一个
IN操作符
SELECT vend_id,prod_name,prod_price
FROM products
WHERE vend_id IN ('DLL01','BRS01')
NOT操作符
SELECT prod_id,prod_price,prod_name
FROM products
WHERE prod_id
NOT BETWEEN 'BR01' AND 'RYL01'