Display all table/column names where value is a specific string

displayNullColumns.sql

DELIMITER $$
DROP PROCEDURE IF EXISTS `displayNullColumns`$$
CREATE PROCEDURE `displayNullColumns`()
  BEGIN
    SET @expression = (
      SELECT GROUP_CONCAT(CONCAT('SELECT ', s._column, ' AS _value, \'', s._column, '\' AS _column, \'', s._table, '\' AS _table FROM ', s._table, ' WHERE ', s._column, ' = \'null\'')
                          SEPARATOR ' UNION ')
      FROM (
             SELECT DISTINCT
               COLUMN_NAME AS `_column`,
               TABLE_NAME  AS `_table`
             FROM INFORMATION_SCHEMA.COLUMNS
             WHERE TABLE_SCHEMA = 'dev_table'
                   AND COLUMN_NAME IS NOT NULL
                   AND TABLE_NAME IS NOT NULL
           ) AS s
    );

    IF @expression IS NOT NULL AND @expression != ''
    THEN
      PREPARE stmt FROM @expression;
      EXECUTE stmt;
    END IF;
  END$$
DELIMITER ;

CALL displayNullColumns();