Procedure UNION on tables - mysql

Question

How can I UNION all results from stmtQuery to ONE RESULTS example results from table basia and Comments_11 .... etc
DELIMITER $$
DROP PROCEDURE IF EXISTS SearchUserY $$
CREATE PROCEDURE `SearchUserY`(IN UserIdValue INT(11) )
BEGIN
DECLARE done INT DEFAULT FALSE;
DECLARE tableName VARCHAR(50);
DECLARE stmtFields TEXT ;
DECLARE columnName VARCHAR(50) default 'UserId';
DECLARE cursor1 CURSOR FOR
SELECT table_name
FROM information_schema.COLUMNS
WHERE table_schema = 'comments'
AND column_name LIKE '%UserId';
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
OPEN cursor1;
read_loop: LOOP
FETCH cursor1 INTO tableName;
IF done THEN
LEAVE read_loop;
END IF;
SET stmtFields = CONCAT('`',tableName,'`','.' , columnName ,'=', UserIdValue) ;
SET #stmtQuery=CONCAT(#sql,'SELECT Nick, Title, Content FROM ' ,'`',tableName,'`', ' WHERE ', stmtFields ) ;
select #stmtQuery;
END LOOP;
PREPARE stmt FROM #stmtQuery ;
EXECUTE stmt ;
DEALLOCATE PREPARE stmt;
CLOSE cursor1;
END
results example (select #stmtQuery):
SELECT Nick, Title, Content FROM `basia` WHERE `basia`.UserId=0
SELECT Nick, Title, Content FROM `Comments_11` WHERE `Comments_11`.UserId=0
... etc
I want get a one results from all this query but know I got only One results

Answer 1

Generate query in a loop using CONCAT function, add 'UNION' or 'UNION ALL' clause between them, then execute result query with a prepared statements.
Solution without cursor:
SET #resultQuery = NULL;
SELECT
GROUP_CONCAT(
DISTINCT
CONCAT('SELECT Nick, Title, Content FROM ', table_name, ' WHERE UserId = ', UserIdValue)
SEPARATOR '\r\nUNION\r\n'
)
INTO
#resultQuery
FROM
information_schema.COLUMNS
WHERE
table_schema = 'comments' AND column_name LIKE '%UserId';
SELECT #resultQuery;
It will produce result like this:
SELECT Nick, Title, Content FROM table1 WHERE UserId = 10
UNION
SELECT Nick, Title, Content FROM table2 WHERE UserId = 10
UNION
SELECT Nick, Title, Content FROM table3 WHERE UserId = 10
UNION
SELECT Nick, Title, Content FROM table4 WHERE UserId = 10
...
Increase group_concat_max_len variable if needed. It is the maximum allowed result length for the GROUP_CONCAT() function, default value = 1024.