Question

How can relise in one query this SELECTs from tables without relationship?

SELECT discount_rate.valueSet, discount_rate.dateSet 
FROM discount_rate 
WHERE discount_rate.dateSet<='2011-12-11' 
ORDER BY discount_rate.dateSet DESC LIMIT 1; 

SELECT min_wage.valueMonth AS min_wage_month, min_wage.valueDay AS min_wage_day 
FROM min_wage 
WHERE min_wage.dateSet<='2011-12-11' 
ORDER BY min_wage.dateSet DESC LIMIT 1;

SELECT max_wage.valueWage 
FROM max_wage 
WHERE max_wage.dateSet<='2011-12-11' 
ORDER BY max_wage.dateSet DESC LIMIT 1;

Answer 1

Since every one of the 3 queries returns one row, you can wrap them in a query with CROSS JOIN:

SELECT valueSet
     , dateSet
     , valueMonth
     , valueWage 
FROM
    ( SELECT ... ) AS q1        --- subquery 1
  CROSS JOIN
    ( SELECT ... ) AS q2        --- subquery 2
  CROSS JOIN
    ( SELECT ... ) AS q3        --- subquery 3