How to Pivot Dynamic Row Values into Column Names in MySQL?

Convert dynamic row values ​​to column names using MySQL

In legacy tables with fixed structures, getting data in pivot format can be a challenge. MySQL lacks native pivot functions and requires the use of prepared statements to solve this problem.

Consider the following legacy table:

<code>id    name       value
------------------------------
0     timezone   Europe/London
0     language   en
0     country    45
0     something  x
1     timezone   Europe/Paris
1     language   fr
1     country    46</code>

Desired output, using dynamic row values ​​as column names:

<code>id    timezone       language    country  something
---------------------------------------------------
0     Europe/London  en          45       x
1     Europe/Paris   fr          46</code>

Unlike other RDBMS, MySQL requires an indirection approach. Building prepared statements is the preferred approach.

SELECT CONCAT(
  'SELECT `table`.id', GROUP_CONCAT('
     ,    `t_', REPLACE(name, '`', '``'), '`.value
         AS `', REPLACE(name, '`', '``'), '`'
     SEPARATOR ''),
 ' FROM `table` ', GROUP_CONCAT('
     LEFT JOIN `table`   AS `t_', REPLACE(name, '`', '``'), '`
            ON `table`.id = `t_', REPLACE(name, '`', '``'), '`.id
           AND `t_', REPLACE(name, '`', '``'), '`.name = ', QUOTE(name)
     SEPARATOR ''),
 ' GROUP BY `table`.id'
) INTO @qry FROM (SELECT DISTINCT name FROM `table`) t;

PREPARE stmt FROM @qry;
EXECUTE stmt;

This query uses GROUP_CONCAT() to build a dynamic SQL statement to connect the necessary JOINs and column aliases. The generated SQL statements are then prepared and executed.

This approach allows using unique row values ​​as variable column names without the need for hard-coded subselects or CASE statements. While it may require more setup, it provides a more flexible and efficient solution for pivoting data in MySQL.

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