MySQL Pivot表子字符串列名称

Question

I have a table structure into MySQL databse which looks like this:

Table data :

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

My desired output is the folowing:

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

I wanted to know if there is any manner to do it with MySQL. The big issue, I have never found any substring function to truncate column names.

Answer 1

you can test my Querys on your DB. You only must setup the first two vars. The Tablename and a Row number that contains the string.

 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;

Test

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)

Please let me know if it works for you