How to select from dynamic table name

Question

I have tables like

changes201101
changes201102
changes201103
...
changes201201

And table whichchanges which contain rows Year and MONTH

How I can select * from changes from whichchanges?

I type this query

SET @b := SELECT CONCAT('changes',year,month) FROM whichchanges;
((((@b should contain now multiple rows of changesYearMonth)))))
SET @x := SELECT * FROM @b;
Prepare stmt FROM @b;
Prepare stmt FROM @x;
Execute stmt;

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT CONCAT('changes',year,month) FROM changes)' at line 1

Solution

You open 1 ( and close 2 ). Remove the last:

SELECT CONCAT('changes',year,month) FROM changes

Edit

the second statement should probably be

SET @x := SELECT * FROM (@b) as b;

That works, but not sure if that is what you want:

SET @b := 'SELECT CONCAT(''changes'',`year`,`month`) FROM whichchanges';
SET @x := 'SELECT * FROM (SELECT CONCAT(''changes'',`year`,`month`) FROM whichchanges) as b';
Prepare stmt FROM @b;
Prepare stmt FROM @x;
Execute stmt;

Edit2

If I understood you right you are looking for that single query:

select * from changes
where change_column in (select distinct concat(`year`, `month`) from whichchanges)

Edit3

select @b := group_concat(concat(' select * from changes', `year`, `month`, ' union ') separator ' ') as w from whichchanges;
set @b := left(@b, length(@b) - 6);

Prepare stmt FROM @b;
Execute stmt;

SQLFiddle example

Comments

[juergen d]

Looks like you edited your question. Now the query doesn't fit to your error message any more.

[breq]

SET @b = SELECT CONCAT('change',year,month) FROM whichchanges; SET @x := SELECT * FROM (@b); Prepare stmt FROM @b; Prepare stmt FROM @x; Execute stmt; #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT CONCAT('changes',year,month) FROM whichchanges' at line 1

[breq]

if i use "SET @b = (SELECT CONCAT('changes',year,month) FROM whichchanges);" **#1242 - Subquery returns more than 1 row ** if i use SET @b = (SELECT CONCAT('changes',year,month) FROM whichchanges LIMIT 1); #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT * FROM (@b)' at line 1

[breq]

i hope this will help i.imgur.com/hni0g.jpg if not, I'll do it by using PHP

[breq]

@jurgen-d, yep, it must be in one query but what is "change_column" in your query? I think that query should be something like "select * from changes where changes in (select distinct concat('changes ',yer, month) from whichchanges)" #1146 - Table 'database.changes' doesn't exist

[juergen d]

You should replace change_column with the column name that holds the values in format 201201 of your changes table.

[juergen d]

@breq: See this SQLFiddle Example. Is that correct? If not, correct it and post back the SQLFiddle link.

[juergen d]

@breq: See my last update with this example.

[breq]

last questions, why i've got comma between union and select? it does not work on my pc :/ #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' select * from changes200804 union , select * from changes200805 union , select * ' at line 1 i've change tab names on my pc, but on sqlfiddle it work fine with my real tab names

[breq]

let us continue this discussion in chat