


MySQL dynamic row value as column name pivot
Question:
In older MySQL tables, your data had mutable column names stored as unique values in a single column named "name". You need a query that converts this data into a pivot format, where the name values become the column headers and the corresponding field values become the values under those headers.
Solution:
Despite the lack of native support for pivots, MySQL can still achieve this through dynamic SQL and the GROUP_CONCAT() function.
MySQL query:
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;
Instructions:
- The subquery selects different name values and generates a UNION query to represent the different column names required for the pivot.
- The CONCAT() function concatenates SQL strings and uses GROUP_CONCAT to dynamically connect column names with their values.
- It creates a temporary stored procedure stmt using the generated SQL string.
- EXECUTE stmt statement executes dynamic SQL queries, pivoting data as expected.
Result:
The query returns a pivoted result set with name values as column headers and field values as corresponding values:
id | timezone | language | country | something |
---|---|---|---|---|
0 | Europe/London | en | 45 | x |
1 | Europe/Paris | fr | 46 | NULL |
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