SQL字段拆分优化
今天看到一条用函数处理连接的SQL,是群里某位网友的,SQL语句以下:
SELECT SO_Order.fdate ,
SO_Order.fsn
FROM so_order
INNER JOIN so_orderitem ON CHARINDEX(so_Orderitem.fid, SO_Order.fid) >= 1
WHERE so_order.FOrderDate = ‘2015-09-06’
语句不算复杂,只是履行比较慢,下面是关于这SQL语句的一些信息:
–1.SQL履行203条数据
–2.耗时12秒
–3.so_order表的fid字段是字符串集合,
–由1⑵个字符串组成,用’,’分隔
SELECT COUNT(*)
FROM SO_Order
WHERE so_order.FOrderDate = ‘2015-09-06’–24
SELECT COUNT(*)
FROM so_Orderitem–414154
通过分析履行计划,so_order和so_orderitem走嵌套循环是正确的,查询的瓶颈是在so_orderitem的索引
扫描上。因此,我们要通过改写SQL,到达so_orderitem走索引查找的目的。
将so_order表的fid字段拆分成2个字段,然后union all成一个结果集,再和so_orderitem关联,便可让so_orderitem表走索引查找。
改写的SQL以下:
;WITH x0
AS ( SELECT fdate ,
fsn ,
LEFT(fid, CASE WHEN CHARINDEX(‘,’, fid, 1) = 0 THEN 0
ELSE CHARINDEX(‘,’, fid, 1) – 1
END) AS fid
FROM so_order
WHERE FOrderDate = ‘2015-09-06’
UNION ALL
SELECT fdate ,
fsn ,
RIGHT(fid, LEN(fid) – CHARINDEX(‘,’, fid, 1)) AS fid
FROM so_order
WHERE FOrderDate = ‘2015-09-06’
)
SELECT SO_Order.fdate ,
SO_Order.fsn
FROM x0 so_order
INNER JOIN so_orderitem ON so_Orderitem.fid = SO_Order.fid
下面是SQL改写后,网友的反馈截图
改写后SQL的履行计划以下:
文章来源:丸子建站
文章标题:SQL字段拆分优化
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