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mysql - 如何排序这个 MySQL 查询

问题描述

我正在尝试在此查询中插入 ORDER BY 以对 Total 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的，但没有运气：

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'

标签： mysqlsqlsql-order-byuniondynamic-sql

解决方案

I think you want:

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');

Rationale: the ORDER BY clause should go after all UNION ALL subqueries - so it needs to be outside of the GROUP_CONCAT(), in an outer CONCAT().

Also please note that you don't need CONCAT() within GROUP_CONCAT(): MySQL does that by default already.

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