Chaining SQL queries - mysql

Question

Right now I'm running
SELECT formula('FOO') FROM table1
WHERE table1.foo = 'FOO' && table1.bar = 'BAR';
but I would like to run this not on the constant FOO but on each value from the query
SELECT foos FROM table2
WHERE table2.bar = 'BAR';
How can I do this?
Edit: Important change: added FOO to the arguments of function.
Illustration:
SELECT foo FROM table1 WHERE foo = 'FOO' && table1.bar = 'BAR';
gives a column with FOOa, FOOb, FOOc.
SELECT formula('FOO') FROM table1
WHERE table1.foo = 'FOO' && table1.bar = 'BAR';
gives a single entry, say sum(FOO) (actually much more complicated, but it uses aggregates at some point to combine the results).
I want some query which gives a column with sum(FOO1), sum(FOO2), ... where each FOOn is computed in like manner to FOO. But I'd like to do this with one query rather than n queries (because n may be large and in any case the particular values of FOOn vary from case to case).

Answer 1

Try this one:
SELECT formula FROM table1
WHERE table1.foo IN(SELECT foos FROM table2
WHERE table2.bar = 'BAR';
) AND table1.bar = 'BAR';

Answer 2

SELECT formula FROM table1 WHERE bar = 'BAR' AND foo IN (SELECT foos FROM table2 WHERE bar = 'BAR');
EDIT:
This isn't tested, but perhaps this will work?
SELECT formula(q1.foo) FROM table1 INNER JOIN (SELECT foo, bar FROM table2) q1 ON table1.foo = q1.foo WHERE table1.bar = 'BAR';

Answer 3

You will have to use dynamic SQL statements.
The way this works is that you just string the SQL statement together using parameters.
You will need to be careful though not to allow users to feed that data, because escaping cannot protect you against SQL-injection. You will need to check every column name against a whitelist.
Here's example code in a stored procedure.
The way this works, is that you have a (temporary) table with column names and the stored procedure builds this into a query:
dynamic /*holds variable parts of an SQL statement
-----------
id integer PK
column_name varchar(255)
operation ENUM('what','from','where','group by','having','order by','limit')
function_name varchar(255) /*function desc with a '#' placeholder where */
/* the column-name goes */
whitelist /*holds all allowed column names*/
-----------
id integer PK
allowed varchar(255) /*allowed column of table name*/
item ENUM('column','table')
Dynamic SQL stored procedure. Expects two tables: dynamic and whitelist to be prefilled.
DELIMITER $$
CREATE PROCEDURE dynamic_example;
BEGIN
DECLARE vwhat VARCHAR(65000);
DECLARE vfrom VARCHAR(65000);
DECLARE vwhere VARCHAR(65000);
DECLARE vQuery VARCHAR(65000);
SELECT group_concat(REPLACE(function_name,'#',column_name)) INTO vwhat
FROM dynamic
INNER JOIN whitelist wl ON (wl.allowed LIKE column_name
AND wl.item = 'column')
WHERE operation = 'what' AND
SELECT group_concat(REPLACE(function_name,'#',column_name)) INTO vfrom
FROM dynamic
INNER JOIN whitelist wl ON (wl.allowed LIKE column_name
AND wl.item = 'table')
WHERE operation = 'from';
SELECT group_concat(REPLACE(function_name,'#',column_name)) INTO vwhere
FROM dynamic
INNER JOIN whitelist wl ON (wl.allowed LIKE column_name
AND wl.item = 'column')
WHERE operation = 'where';
IF vwhat IS NULL THEN SET vwhat = ' * ';
IF vwhere IS NOT NULL THEN SET vwhere = CONCAT(' WHERE ',vwhere); END IF;
SET vQuery = CONCAT(' SELECT ',vwhat,' FROM ',vfrom,IFNULL(vwhere,''));
PREPARE dSQL FROM vQuery;
EXECUTE dSQL;
DEALLOCATE PREPARE dSQL;
END $$
DELIMITER ;

Answer 4

Try:
SELECT formula FROM table1, table2
WHERE table1.foo = table2.foo AND table1.bar = table2.bar;