表:
订单表 t_order (索引id) 200W条
订单明细表 t_order_detail( 索引 order_id) 1500W条
统计:每个订单下有多个商品常用a:
SELECT
a.id AS '订单号',
COUNT(b.id) AS '商品数量'
FROM t_order a
LEFT JOIN
t_order_detail b ON
a.id=b.order_id
GROUP BY a.id还有这个b:
SELECT a.id as '订单号',
( SELECT COUNT(1) FROM t_order_detail b WHERE a.id=b.order_id) AS '商品数量'
FROM t_order AS a
那个好?b里面没写group by。
订单表 t_order (索引id) 200W条
订单明细表 t_order_detail( 索引 order_id) 1500W条
统计:每个订单下有多个商品常用a:
SELECT
a.id AS '订单号',
COUNT(b.id) AS '商品数量'
FROM t_order a
LEFT JOIN
t_order_detail b ON
a.id=b.order_id
GROUP BY a.id还有这个b:
SELECT a.id as '订单号',
( SELECT COUNT(1) FROM t_order_detail b WHERE a.id=b.order_id) AS '商品数量'
FROM t_order AS a
那个好?b里面没写group by。
正迎了那句话:有left join,就不要使用多表
a:b:b加上group by之后