MySQL SUM，join和union 4表

Question

I have 4 tables with similar column name:

 Table 1 : simp_wajib id anggota nilai 1 nama1 100 2 nama2 100 3 nama1 100 Table 2 : simp_pokok id anggota nilai 1 nama2 100 2 nama3 100 3 nama1 100 Table 3 : simp_sukarela id anggota nilai 1 nama2 100 2 nama2 100 3 nama1 100 Table 4 : simp_berjangka id anggota nilai 1 nama3 100 2 nama2 100 3 nama3 100 

I try to join the four tables with following query but it give me incorrect sum value

 SELECT nama.anggota, sum(simp_wajib.nilai) as wajib, sum(simp_pokok.nilai) as pokok,sum(simp_sukarela.nilai) as sukarela,sum(simp_berjangka.nilai) as berjangka FROM (SELECT anggota from simp_pokok UNION SELECT anggota FROM simp_wajib) nama LEFT JOIN simp_pokok ON simp_pokok.anggota=nama.anggota LEFT JOIN simp_wajib ON simp_wajib.anggota=nama.anggota LEFT JOIN simp_sukarela ON simp_sukarela.anggota=nama.anggota LEFT JOIN simp_berjangka ON simp_berjangka.anggota=nama.anggota group by nama.anggota 

Any help would be appreciated

Answer 1

If you join the tables, you will end up with more lines than you expect, because the join will cross the values between the tables. What you probably need, is a union between all your tables, to summarize the common values, grouped by the common column first, and then from a custom field you will add to keep track of the origin table.

Finally, you will transpose the results with a CASE statement.

select anggota, 
sum(CASE WHEN origin = 'simp_pokok' THEN nilai END) `simp_pokok`,
sum(CASE WHEN origin = 'simp_wajib' THEN nilai END) `simp_wajib`,
sum(CASE WHEN origin = 'simp_sukarela' THEN nilai END) `simp_sukarela`,
sum(CASE WHEN origin = 'simp_berjangka' THEN nilai END) `simp_berjangka`
from (
    SELECT nama.anggota, sum(nilai) as nilai, origin
    FROM
    (SELECT anggota, nilai, 'simp_pokok' as origin from simp_pokok
     UNION ALL
     SELECT anggota, nilai, 'simp_wajib' as origin FROM simp_wajib
     UNION ALL
     SELECT anggota, nilai, 'simp_sukarela' as origin FROM simp_sukarela
     UNION ALL
     SELECT anggota, nilai, 'simp_berjangka' as origin FROM simp_berjangka
    ) nama
    group by nama.anggota, nama.origin) united
group by anggota

if you don't like the "null" values, you can wrap the sum() with a coalesce function, like

coalesce(sum(CASE ...), 0) as `simp_pokok`

Answer 2

With your query, the result is as follow

 anggota nilai origin 1 200 simp_berjangka 1 200 simp_pokok 1 100 simp_sukarela 1 400 simp_wajib 2 300 simp_sukarela 2 500 simp_wajib 3 100 simp_pokok 3 200 simp_sukarela 4 200 simp_berjangka 

My expected output is each sum value which is grouped by anggota become a column

 anggota sum(simp_pokok) sum(simp_wajib) sum(simp_berjangka) sum(simp_sukarela) 1 200 400 200 200 2 0 500 0 300 3 100 0 0 200 4 0 0 200 0