MySQL Pivot表子字符串列名称

Question

我有一个到MySQL数据库的表结构，如下所示：

表数据 ：

Ref  | Var | 3SAa combined % | 3SAa combined of | 3SAa Forward of |3SAa Forward % | 3SAa reverse % | 3SAa Forward of|
---------------------------------------------------------------------------------------------------------------------
AL23    TT   0.00              38.78              48.39             100.0            12.01             85.3

我期望的输出如下：

ID   | Ref  |Var |a combined % | a combined of | a Forward of |a Forward % | a reverse % | a Forward of|
--------------------------------------------------------------------------------------------------------
3SA   AL23    TT    0.00              38.78         48.39         100.0        12.01             85.3

我想知道MySQL是否有任何方法可以做到这一点。 最大的问题是，我从未找到任何子字符串函数来截断列名。

Answer 1

您可以在数据库上测试我的查询。 您只需设置前两个变量。 表名和包含字符串的行号。

 SET @table_name = 'mytab';
 SET @col_id = 3;

 SELECT DATABASE() INTO @dbname;

 SELECT SUBSTRING_INDEX(COLUMN_NAME,' ' , 1)  INTO @id_name
 FROM information_schema.columns
  WHERE table_schema = @dbname 
   AND TABLE_NAME = @table_name
   AND ORDINAL_POSITION = @col_id;

 SELECT CONCAT('SELECT \'', @id_name, '\' AS Id, ' , GROUP_CONCAT(
     CONCAT( '`',COLUMN_NAME,'`')
     , ' AS `', REPLACE(COLUMN_NAME,CONCAT(@id_name,' ') , '')
     ,'`\n' ), ' FROM ', @table_name) INTO @sql
  FROM information_schema.columns
  WHERE table_schema = @dbname 
   AND TABLE_NAME = @table_name
  ORDER BY ORDINAL_POSITION; 

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

测试

MariaDB []> SELECT * FROM mytab;
+------+------+-----------------+------------------+
| Ref  | Var  | 3SAa combined % | 3SAa combined of |
+------+------+-----------------+------------------+
| AL23 |      | 0.00            | 38.78            |
+------+------+-----------------+------------------+
1 row in set (0.00 sec)

MariaDB []>  SET @table_name = 'mytab';
Query OK, 0 rows affected (0.00 sec)

MariaDB [bernd]>  SET @col_id = 3;
Query OK, 0 rows affected (0.00 sec)

MariaDB []>  SELECT DATABASE() INTO @dbname;
Query OK, 1 row affected (0.00 sec)

MariaDB []>  SELECT SUBSTRING_INDEX(COLUMN_NAME,' ' , 1)  INTO @id_name
    ->  FROM information_schema.columns
    ->   WHERE table_schema = @dbname
    ->    AND TABLE_NAME = @table_name
    ->    AND ORDINAL_POSITION = @col_id;
Query OK, 1 row affected (0.01 sec)

MariaDB []>  SELECT CONCAT('SELECT \'', @id_name, '\' AS Id, ' , GROUP_CONCAT(
    ->      CONCAT( '`',COLUMN_NAME,'`')
    ->      , ' AS `', REPLACE(COLUMN_NAME,CONCAT(@id_name,' ') , '')
    ->      ,'`\n' ), ' FROM ', @table_name) INTO @sql
    ->   FROM information_schema.columns
    ->   WHERE table_schema = @dbname
    ->    AND TABLE_NAME = @table_name
    ->   ORDER BY ORDINAL_POSITION;
Query OK, 1 row affected (0.01 sec)

MariaDB []> PREPARE stmt FROM @sql;
Query OK, 0 rows affected (0.00 sec)
Statement prepared

MariaDB []> EXECUTE stmt;
+------+------+------+------------+-------------+
| Id   | Ref  | Var  | combined % | combined of |
+------+------+------+------------+-------------+
| 3SAa | AL23 |      | 0.00       | 38.78       |
+------+------+------+------------+-------------+
1 row in set (0.00 sec)

MariaDB []> DEALLOCATE PREPARE stmt;
Query OK, 0 rows affected (0.00 sec)

请让我知道它是否适合您