MYSQL query using variable as table name in LEFT JOIN

Question

SELECT var1,var2,var3,table_name 
FROM table1 LEFT JOIN table_name on var3=table_name.id

Meaning I want to dynamically left join table, depending o

Answer 1

Another way is to unite all tables with a union query:

SELECT *, 44 as table_origin FROM `Table_44`
UNION ALL
SELECT *, 58 as table_origin FROM `Table_58`;

You could even prepare that as view:

CREATE VIEW `AllTheTables` AS
SELECT *, 42 as table_origin FROM `Table_42`
UNION ALL
SELECT *, 44 as table_origin FROM `Table_44`
UNION ALL
SELECT *, 58 as table_origin FROM `Table_58`
UNION ALL
SELECT *, 69 as table_origin FROM `Table_69`;

And thus query it safely:

SELECT * FROM AllTheTables WHERE table_origin IN (44,58) AND something = 'foobar';
-- or --
SELECT * FROM AllTheTables WHERE table_origin = 42 AND something = 'the question';

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In your exact case it could look like this:

SELECT var1, var2, var3, table_name 
FROM table1 LEFT JOIN AllTheTables ON table1.var3=AllTheTables.table_origin

Answer 2

Table names, as well as column names, can't be dynamic in an SQL query. So you have to apply your logic programmatically, using 2 queries, or with a stored procedure, see an example here: http://forums.mysql.com/read.php?98,126506,126598#msg-126598