Mysql query using inner join

Question

I have the following table t

id   a   b    c
1    1   1    1
2    2   1    1

and the table t1

id  a   b   c  p
1  1    1   1   47 
2  1    1   1   2
3  2    1   1   78

My purpose is to get a table

    id   a   b    c  p 
    1    1   1    1  49
    2    2   1    1  78

I tried the following script but it not works @y=@y+t1.p is always null :

select t.id,t1.a, t1.b , t1.c ,@y=@y+t1.p from t1
inner join t
where t.a=t1.a
and t.b=t1.b
and t.c=t1.c

For more details enter link description here

Answer 1

This gives the result you want:

select t.id,
       t1.a, 
       t1.b , 
       t1.c ,
       SUM(t1.p) from t1
inner join t ON t.a=t1.a and t.b=t1.b and t.c=t1.c
group by t.id, t1.a, t1.b, t1.c

sqlfiddle demo

This uses SUM and GROUP BY. Make sure you use all the columns from the select in the GROUP BY to avoid undesired results.

Answer 2

You need to add the GROUP BY statement and use SUM

SELECT
  t.id,
  t1.a, 
  t1.b, 
  t1.c,
  SUM(t1.p) AS p
FROM 
  t1
  INNER JOIN t
     USING (a, b, c)
GROUP BY a, b, c

You can see it running here . It is possible to do it with variables but type of problem is usually solved with aggregate functions.

Answer 3

Try using sum() function over group by and colease . Plenty of examples in google.

One link is here

Answer 4

The calculation part needs to be done this way (if you need it sometime again)

SET @y = 0;

select t.id,t1.a, t1.b , t1.c ,(@y:=@y + t1.p) from t1
inner join t
where t.a=t1.a
and t.b=t1.b
and t.c=t1.c
;

see demo http://www.sqlfiddle.com/#!2/68a61/8