LIMIT 1是否有任何性能提升？

Question

LIMIT 1查询后追加是否有任何性能提升？

...如果只有一个匹配的可能条目(WHERE主键的子句)？

SELECT `x`
FROM `unicorns`
WHERE `id` = 123
LIMIT 1

......同样的,但现在是DELETE:

DELETE FROM `unicorns`
WHERE `id` = 123
LIMIT 1

......和UPDATE:

UPDATE `unicorns`
SET `rainbows` = `rainbows` + 1
WHERE `id` = 123
LIMIT 1

PS Column id是主键,所以它是独一无二的.

谢谢你的建议!

Answer 1

这取决于您是否在列上有索引

DELETE FROM `unicorns` WHERE `id` = 123 LIMIT 1

如果 id 是主键则毫无意义，但是

DELETE FROM `unicorns` WHERE `noindexoclumn` = 123 LIMIT 1

会给你性能提升