怎么把这样一个表儿
year month amount
1991 1 1.1
1991 2 1.2
1991 3 1.3
1991 4 1.4
1992 1 2.1
1992 2 2.2
1992 3 2.3
1992 4 2.4
查成这样一个结果
year m1 m2 m3 m4
1991 1.1 1.2 1.3 1.4
1992 2.1 2.2 2.3 2.4
------解决方案--------------------
这不是行列转换吗，a表示表名
SELECT
YEAR,
SUM(IF(MONTH=1,amount,0)) AS m1,
SUM(IF(MONTH=2,amount,0)) AS m2,
SUM(IF(MONTH=3,amount,0)) AS m3,
SUM(IF(MONTH=4,amount,0)) AS m4
FROM a
GROUP BY YEAR
------解决方案--------------------
SELECT
YEAR,
SUM(CASE MONTH WHEN 1 THEN amount ELSE 0 END) AS m1,
SUM(CASE MONTH WHEN 2 THEN amount ELSE 0 END) AS m2,
SUM(CASE MONTH WHEN 3 THEN amount ELSE 0 END) AS m3,
SUM(CASE MONTH WHEN 4 THEN amount ELSE 0 END) AS m4
FROM a
GROUP BY YEAR
用 case when zhen 的语法也可以，结果一样，这个数据是死的 ，如果数据是动态的就不行了。。
就必须用变量了
------解决方案--------------------
select a.year,sum(if(a.month='1',amount,'0')) as 'm1',
sum(if(a.month='2',amount,0)) as 'm2',
sum(if(a.month='3',amount,0)) as 'm3',
sum(if(a.month='4',amount,0)) as 'm4'
from row_column_test a
group by a.year;
------解决方案--------------------
- SQL code
CREATE TABLE t1( nian INT, yue INT, amount DECIMAL(18,1))INSERT INTO t1SELECT 1991, 1, 1.1 UNION ALLSELECT 1991, 2, 1.2 UNION ALLSELECT 1991, 3, 1.3 UNION ALLSELECT 1991, 4, 1.4 UNION ALLSELECT 1992, 1, 2.1 UNION ALLSELECT 1992, 2, 2.2 UNION ALLSELECT 1992, 3, 2.3 UNION ALLSELECT 1992, 4, 2.4SELECT * FROM t1DECLARE @str VARCHAR(8000)SET @str='select nian'SELECT @[email protected]+',max(case when yue='+LTRIM(yue)+' then amount else 0 end) as ['+LTRIM(yue)+']'FROM (SELECT DISTINCT yue FROM t1) AS a1SET @[email protected]+' from t1 group by nian'PRINT @strEXEC (@str)-----------------nian 1 2 3 41991 1.1 1.2 1.3 1.41992 2.1 2.2 2.3 2.4
------解决方案--------------------
字段名调整了下
- SQL code
DECLARE @str VARCHAR(8000)SET @str='select nian'SELECT @[email protected]+',max(case when yue='+LTRIM(yue)+' then amount else 0 end) as [m'+LTRIM(yue)+']'FROM (SELECT DISTINCT yue FROM t1) AS a1SET @[email protected]+' from t1 group by nian'PRINT @strEXEC (@str)---------------------nian m1 m2 m3 m41991 1.1 1.2 1.3 1.41992 2.1 2.2 2.3 2.4