Question

我想在MySQL中创建交叉表。

有两个表TABL1和TBL2，我不知道如何将列转换为行。

请给我一个解决方案。

我的编码如下：

选择*来自TBL1 t1左连接TBL2 t2 on t1.des = t2.des;

TBL1 :
DES
A
C
D
E

TBL2
ID DES
1  A
2  C
3

RESULT THAT I NEED

ID   A   C  D  E
1    1
2        1
3

此致

Answer 1

试试这个：

SELECT
    t2.id,
    SUM(IF(t1.des IS NOT NULL AND t1.des = 'A',1,0)) as 'A',
    SUM(IF(t1.des IS NOT NULL AND t1.des = 'C',1,0)) as 'C',
    SUM(IF(t1.des IS NOT NULL AND t1.des = 'D',1,0)) as 'D',
    SUM(IF(t1.des IS NOT NULL AND t1.des = 'E',1,0)) as 'E'
FROM
    TBL2 t2
LEFT JOIN TBL1 t1
    ON t2.des = t1.des
GROUP BY
    t2.id

Answer 2

对于某些自动化，您可以尝试使用后续步骤：

制作一个光标来读取你的TBL1 - 这样你就会知道你有多少cols
```
DECLARE curs CURSOR FOR SELECT des FROM TBL1;
```

在游标内部，您需要为Select语句创建dynamicSQL。像这样：

....
FETCH curs INTO cDes;
....
set @sel = concat(@sel, 
', SUM(IF(t1.des IS NOT NULL AND t1.des = ''', cDes,''',1,0)) as ''',cDes, '''');
...
CLOSE curs;

完成后，您需要完成动态SQL的完整版本。像这样的东西：

set @crosstab = concat('select t2.id', @sel, 
                        'FROM TBL2 t2
                        LEFT JOIN TBL1 t1 ON t2.des = t1.des
                        GROUP BY t2.id');

PREPARE STMT FROM @crosstab;
EXECUTE STMT;
DEALLOCATE PREPARE STMT;

在mysql中将列转换为行交叉表

2 个答案: