Question

我在MySql中有两个表，

shareholders     

    id  name   value
     1  harry    20
     2  mark     60
     3  richard  20

第二个表是

transactions    
     id   date          amount
      1   2013-11-01    2000
      2   2013-11-01    150
      3   2013-11-01    300
      4   2013-11-02    700
      5   2013-11-02    5400

第一个表包含交易金额的百分比。是否有可能在MySQL中有一个选择查询将返回以下输出？

transid    amount    harry   mark   richard ,.....
1          2000      400     1200    400
2          150        30       90     30
3          300        60      180     60
.
.
.

股东人数不固定

Answer 1

为此使用动态SQL

SET @sql = NULL;

SELECT GROUP_CONCAT(CONCAT(
          'MAX(CASE WHEN h.id = ', id, 
          ' THEN amount * ', value / 100, 
          ' END) `', name, '`'))
  INTO @sql
  FROM shareholders;

SET @sql = CONCAT(
              'SELECT t.id transaction_id, t.date, t.amount, ', @sql, 
              '  FROM transactions t CROSS JOIN shareholders h 
                GROUP BY t.id');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

输出：

| TRANSACTION_ID |       DATE | AMOUNT | HARRY | MARK | RICHARD |
|----------------|------------|--------|-------|------|---------|
|              1 | 2013-11-01 |   2000 |   400 | 1200 |     400 |
|              2 | 2013-11-01 |    150 |    30 |   90 |      30 |
|              3 | 2013-11-01 |    300 |    60 |  180 |      60 |
|              4 | 2013-11-02 |    700 |   140 |  420 |     140 |
|              5 | 2013-11-02 |   5400 |  1080 | 3240 |    1080 |

这是 SQLFiddle 演示

为了简化调用端的内容，您可以将其包装在存储过程中

DELIMITER $$
CREATE PROCEDURE shareholders_report()
BEGIN
  SET @sql = NULL;

  SELECT GROUP_CONCAT(CONCAT(
            'MAX(CASE WHEN h.id = ', id, 
            ' THEN amount * ', value / 100, 
            ' END) `', name, '`'))
    INTO @sql
    FROM shareholders;

  SET @sql = CONCAT(
                'SELECT t.id transaction_id, t.date, t.amount, ', @sql, 
                '  FROM transactions t CROSS JOIN shareholders h 
                  GROUP BY t.id');

  PREPARE stmt FROM @sql;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
END$$
DELIMITER ;

然后使用它：

CALL shareholders_report();

这是 SQLFiddle 演示

选择行值为mysql select中的列标题

1 个答案: