Question

I have this Mysql scenario

table1
--------------
id   `7`   `8`
--------------
1    10    20
2    20    30

table 2
---------------
id  code   rel
---------------
3     7     1
4     8     2

I am using following statement to get values

SELECT t2.id, t2.code, 
CASE t2.code WHEN 7 THEN (SELECT `7` FROM table1 t1 where t1.id = t2.rel)
CASE t2.code WHEN 8 THEN (SELECT `8` FROM table1 t1 where t1.id = t2.rel) 
END as val
FROM table2 t2

but it’s neither pretty or functional, because I need these values summed, multiplied, etc, and there are a lot of columns.

Is there a way to join these tables and get table1.7 value for t2.rel,t2.code values?
Something similar to

SELECT t2.id, t2.code, eval(t1.(t2.code))  as val
FROM table2 t2 
JOIN table1 t1 on t2.rel = t1.id

Thank you very much!

Answer 1

I don’t know if it is still relevant.

As you alredy know, there is no such thing as pivot in MySql, but aggregations might look rather easy if the number of columns is defined:

SELECT
  SUM(IF(t2.code = 7, `7`, NULL)) as sum7,
  AVG(IF(t2.code=8, `8`, NULL)) as avg8
FROM t1 JOIN t2
  ON t1.id = t2.rel;