如何对此 MySQL 查询进行排序

Question

我正在尝试在此查询中插入 ORDER BY 以对总计列进行排序：

SELECT GROUP_CONCAT(CONCAT('SELECT ''', COLUMN_NAME,''' MyColumns, SUM(`', COLUMN_NAME,'`) Total FROM mydb.source_table') SEPARATOR '\n UNION ALL \n')
INTO @sql
FROM  INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = 'mydb' 
  AND TABLE_NAME   = 'source_table'
  AND COLUMN_NAME NOT IN ('ID', 'Name');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DROP PREPARE stmt;

结果如下：

+-----------+-----------+
| MyColumns |   Total   |
+-----------+-----------+
| ABC       |     67.00 |
+-----------+-----------+
| DEF       |     40.00 |
+-----------+-----------+
| GHI       |     33.00 |
+-----------+-----------+
| JKL       |     39.00 |
+-----------+-----------+
| MNO       |     33.00 |
+-----------+-----------+

这是我到目前为止尝试过但没有成功的方法：

1. mydb.source_table ORDER BY Total
2. SEPARATOR '\nUNION ALL\n' ORDER BY 'Total' ASC
3. SEPARATOR '\nUNION ALL\n ORDER BY Total' ASC
4. AND COLUMN_NAME NOT IN ('ID', 'Name') ORDER BY 'Total' ASC;
5. ORDER BY 'Total' ASC SEPARATOR '\nUNION ALL\n'

Answer 1

我想你想要：

SELECT CONCAT(
    GROUP_CONCAT(
        'SELECT ''', COLUMN_NAME,''' MyColumns, SUM(`', COLUMN_NAME,'`) Total FROM mydb.source_table' 
        SEPARATOR '\n UNION ALL \n'
    ),
    '\nORDER BY Total DESC'
)
INTO @sql
FROM  INFORMATION_SCHEMA.COLUMNS
WHERE 
    TABLE_SCHEMA = 'mydb' 
    AND TABLE_NAME   = 'source_table'
    AND COLUMN_NAME NOT IN ('ID', 'Name');

基本原理：ORDER BY 子句应该在之后所有 UNION ALL 子查询 - 所以它需要在 GROUP_CONCAT() 之外，在外部 CONCAT().

另请注意，您不需要 CONCAT() GROUP_CONCAT()：MySQL 默认情况下已经这样做了。

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