準備されたステートメントを使用して動的 MySQL ピボット テーブル クエリを作成する方法

-- Initialize @sql variable
SET @sql = NULL;

-- Dynamically create the query string by iterating over distinct `fieldname` values
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'MAX(IF(pa.fieldname = ''',
      fieldname,
      ''', pa.fieldvalue, NULL)) AS ',
      fieldname
    )
  ) INTO @sql
FROM product_additional;

-- Concatenate the constructed string with the base query
SET @sql = CONCAT('SELECT p.id
                    , p.name
                    , p.description, ', @sql, ' 
                   FROM product p
                   LEFT JOIN product_additional AS pa 
                    ON p.id = pa.id
                   GROUP BY p.id, p.name, p.description');

-- Prepare the query
PREPARE stmt FROM @sql;

-- Execute the prepared query
EXECUTE stmt;

-- Deallocate the prepared statement
DEALLOCATE PREPARE stmt;