server|sqlserver|技巧
有表 tableA 如下：-----------------------------------------------------id, type , countNumber , countDate1 A 10 2005-02-01 21:23:342 B 8 2005-02-01 21:23:343 C 5 2005-02-01 21:23:344 B 4 2005-02-01 11:23:345 C 5 2005-02-01 22:23:346 A 11 2005-02-02 12:23:347 B 9 2005-02-02 14:23:348 C 8 2005-02-02 17:23:349 A 15 2005-02-02 19:23:3410 C 6 2005-02-02 04:23:3411 A 7 2005-02-03 1:23:3412 B 11 2005-02-03 2:23:3413 C 12 2005-02-03 5:23:34.......................
想要用一条语句生成如下的报表
日期 类型A 类型B 类型C 2005-02-01 10 12 10 2005-02-02 26 9 14 2005-02-03 7 11 12
我用的是如下的sql语句:
SELECT a.DATEFMT ,(select sum(*) from tableA where type='A' and convert(char(10),countDate,20)= a.DATEFMT) typeA ,(select sum(*) from tableA where type='B' and convert(char(10),countDate,20)= a.DATEFMT) typeB ,(select sum(*) from tableA where type='C' and convert(char(10),countDate,20)= a.DATEFMT) typeC
FROM ( SELECT convert(char(10),countDate,20) DATEFMT FROM tableA GROUP BY convert(char(10),countDate,20)) a
但是这条语句在sqlserver 上执行起来特别的慢，要很久(20多秒)，tabelA 中有9万条数据. 而我在mySql(表中有2万条数据)上执行就快很多！
后来在论坛上看到高手这样写
select convert(char(10),countDate,20),typeA=sum(case type when A then CountNumber else 0 end),typeB=sum(case type when B then CountNumber else 0 end),typeC=sum(case type when C then CountNumber else 0 end)From tableAgroup by convert(char(10),countDate,20)
只用 1秒 不到！ 唉！ 厉害厉害！