sql優化 轉

1. LIMIT優化

當返回的_offset_很大，且字段數比較多的時候，效果尤爲明顯。

SELECT * FROM crm_customer 
WHERE crm_customer_id IN (
	(
		SELECT crm_customer_id FROM (
			SELECT crm_customer_id FROM crm_customer 
			ORDER BY crm_create_time DESC 
			LIMIT 10000, 10
		)t
	)
)