Question

What I’d like to do is execute a MySQL query containing a where clause (“result query”) that is stored in a column in the database. This column, containing the query, is a result of another query (“original query”).

The catches:

• The result query’s where clause can contain a variable value (or two)
• I don’t know what the result query will be when executing the original query, so I cannot pass along the variable’s value

(The list of result queries as well as the variables in the where clauses will be defined by me, so I will will have a list of all the possible variables.)

Essentially, I need to be able to correlate that variable with any number of other values, one example: a user_id, within the database.

original_query_table      | result_query_table
--------------------------------------------------------------
other_id result_query_id  | result_query_id  result_query
1        1                  1                "SELECT ... WHERE user_id = :id "   

I know how to do this with two separate queries, but the question is whether this is possible with only one query?

Answer 1

I would do something like this:

SELECT 'select * from table_a where col_a = ?' INTO @query, 1 into @param1 FROM dual;
PREPARE stmt FROM @query;
EXECUTE stmt USING @param1 ;

So converting that into your tables, I guess would look like:

SELECT a.result_query INTO @query, b.result_query_id INTO @param1 FROM result_query_table a, original_query_table b where a.result_query_id = b.result_query_id;
PREPARE stmt FROM @query;
EXECUTE stmt USING @param1 ;

Will you know how many parameters the where clause will need? If that’s dynamic, then things could get a bit tricky.