MYSQL How to UNION Multiple "Unknown" Tables - mysql

Question

I have some History Tables with Structure of "TableNameYYMM"
How can I UNION all History Tables which Starts with "TableName"?
I need a search over all History Tables.
I tryed it with PREPARE Execute and DEALLOCATE.
But i get everytime a SQL Error.
SET group_concat_max_len = 2048;
SET #startQuery = (SELECT CONCAT('SELECT col1, col2, col3 FROM ',TABLE_SCHEMA,'.', TABLE_NAME)
FROM information_schema.tables
WHERE
ENGINE = 'MyISAM'
AND TABLE_NAME like 'hist%'
ORDER BY TABLE_NAME
LIMIT 0,1);
SET #subquery = (SELECT GROUP_CONCAT(#startquery, 'UNION ALL SELECT col1, col2, col3 FROM ',TABLE_SCHEMA,'.', TABLE_NAME)
FROM information_schema.tables
WHERE
ENGINE = 'MyISAM'
AND TABLE_NAME like 'hist%'
ORDER BY TABLE_NAME
LIMIT 1,1000);
PREPARE stmt1 FROM '? AS combinedTable';
EXECUTE stmt1 USING #subquery;
DEALLOCATE PREPARE stmt1;
On Part 1 (#startquery) i try to get the first part of the Query
"select xxx from table1"
On Part 2 (#subquery) I tried to get all unions (from table2-max 1000)
select xxx from table1
UNION ALL select xxx from table2
UNION ALL select xxx from table3
...
I hope someone have an idea about this problem.

Answer 1

/*
create table history1701 (id int,col1 int,col2 int);
create table history1702 (id int,col1 int,col2 int);
create table history1703 (id int,col1 int,col2 int);
create table history1704 (id int,col1 int,col2 int);
insert into history1701 values (1,1,1);
insert into history1702 values (2,2,2);
insert into history1703 values (3,3,3);
insert into history1704 values (4,4,4);
*/
SET #startQuery = (SELECT CONCAT('SELECT col1, col2 FROM ',TABLE_SCHEMA,'.', TABLE_NAME)
FROM information_schema.tables
WHERE
# ENGINE = 'MyISAM' AND
TABLE_NAME like 'hist%17%'
ORDER BY TABLE_NAME
LIMIT 0,1);
SET #subquery = (
SELECT group_CONCAT(' UNION ALL SELECT col1, col2 FROM ',TABLE_SCHEMA,'.', TABLE_NAME order by table_name separator ' ' )
FROM information_schema.tables
WHERE
TABLE_NAME like 'hist%17%'
and table_name <> (
select table_name from information_schema.tables WHERE
# ENGINE = 'MyISAM' AND
TABLE_NAME like 'hist%17%'
ORDER BY TABLE_NAME
LIMIT 0,1
)
);
select #startquery;
set #subquery = concat(#startquery,#subquery);
PREPARE stmt1 FROM #subquery;
EXECUTE stmt1 ;
DEALLOCATE PREPARE stmt1;
In your code The limit 1,1000 in the first set #subquery returns a null value (not good) and generates a comma after each union all (also not good). I have amended this to exlude the first history table and changed the group concat separator to a space and moved the order by to within the group_concat.