表A (a b c)UPDATE A SET a = '1'
WHERE b =
(SELECT b FROM A WHERE c = '-1')
AND c<> '-1'
UPDATE A SET a= '1'
WHERE b in
(SELECT b FROM A WHERE c = '-1')
AND c <> '-1'想问下 这里的 = 和 in 有什么区别啊执行结果一样吗那个效率高点啊
WHERE b =
(SELECT b FROM A WHERE c = '-1')
AND c<> '-1'
UPDATE A SET a= '1'
WHERE b in
(SELECT b FROM A WHERE c = '-1')
AND c <> '-1'想问下 这里的 = 和 in 有什么区别啊执行结果一样吗那个效率高点啊
in可以有多个值.当只有一个唯一的值时,= 和 in功能一样.
只能等于一个值
in
可以是很多值:in(1,2,3,4)
那么 SELECT b FROM A WHERE c = '-1' 的返回结果 如果不是唯一的值 执行结果 一样吗