同样一条语句，不同写法效率高10倍



#查询自2010-12-1 到 2011-2-28延期三天以上没有发货
SELECT DISTINCT user_id
FROM order_info
WHERE order_id IN
    (
    SELECT order_id FROM shipping_package 
    WHERE add_time  < shipping_time 
    OR shipping_status = 0
    )
AND add_time >= (UNIX_TIMESTAMP('2010-12-01 00:00:00')-28800)
AND add_time <= (UNIX_TIMESTAMP('2011-02-28 23:59:59')-28800)


#查询自2010-12-1 到 2011-2-28延期三天以上没有发货 效率高的写法
SELECT DISTINCT oi.user_id
FROM order_info oi
 RIGHT JOIN
    (
    SELECT order_id FROM shipping_package 
    WHERE add_time  < shipping_time 
    OR shipping_status = 0
    ) AS bb ON bb.order_id=oi.order_id
    WHERE 
 add_time >= (UNIX_TIMESTAMP('2010-12-01 00:00:00')-28800)
AND add_time <= (UNIX_TIMESTAMP('2011-02-28 23:59:59')-28800)