解析SQLServer任意列之间的聚合
(编辑:jimmy 日期: 2024/12/23 浏览:3 次 )
sql的max之类的聚合函数只能针对同一列的n行运算,如果对n列运算,一般都用case 语句来判断,如果列少还比较容易写,列多了就麻烦了。
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/*
测试名称:利用 XML 求任意列之间的聚合
测试功能:对一张表的列数据做 min 、 max 、 sum 和 avg 运算
运行原理:字段合并为 xml 后做 xquery 查询转为行集后聚合
*/
-- 建立测试环境
declare @t table (
id smallint ,
a smallint , b smallint ,
c smallint , d smallint ,
e smallint , f smallint )
insert into @t
select 1, 1, 2, 3, 4, 6, 7 union all
select 2, 34, 45, 56, 54, 9, 6
-- 测试语句
select a.*, c.*
from @t a outer apply(
select doc=(
select * from @t as doc where id= a. id for xml path ( '' ), type )
) b
outer apply(
select
min ( r) as minValue,
max ( r) as maxValue,
sum ( r) as sumValue,
avg ( r) as avgValue
from (
select cast ( cast ( d. n. query( 'text()' ) as varchar ( max )) as int ) as r
from doc. nodes( '/a,b,c,d,e,f' ) D( n)) tt
) c
/* 测试结果
id a b c d e f minValue maxValue sumValue avgValue
------ ------ ------ ------ ------ ------ ------ ----------- ----------- ----------- -----------
1 1 2 3 4 6 7 1 7 23 3
2 34 45 56 54 9 6 6 56 204 34
*/
--------------------------------------------------------------------------------
/*
测试名称:利用 XML 求任意列之间的聚合
测试功能:对一张表的列数据做 min 、 max 、 sum 和 avg 运算
运行原理:字段合并为 xml 后做 xquery 查询转为行集后聚合
*/
-- 建立测试环境
declare @t table (
id smallint ,
a smallint , b smallint ,
c smallint , d smallint ,
e smallint , f smallint )
insert into @t
select 1, 1, 2, 3, 4, 6, 7 union all
select 2, 34, 45, 56, 54, 9, 6
-- 测试语句
select a.*, c.*
from @t a outer apply(
select doc=(
select * from @t as doc where id= a. id for xml path ( '' ), type )
) b
outer apply(
select
min ( r) as minValue,
max ( r) as maxValue,
sum ( r) as sumValue,
avg ( r) as avgValue
from (
select cast ( cast ( d. n. query( 'text()' ) as varchar ( max )) as int ) as r
from doc. nodes( '/a,b,c,d,e,f' ) D( n)) tt
) c
/* 测试结果
id a b c d e f minValue maxValue sumValue avgValue
------ ------ ------ ------ ------ ------ ------ ----------- ----------- ----------- -----------
1 1 2 3 4 6 7 1 7 23 3
2 34 45 56 54 9 6 6 56 204 34
*/
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