Most efficient way to SELECT and JOIN these tables - sql

Question

I have 4 tables:
Table1(Groups):
id_group name_group
1 abc
2 def
3 ghi
Table2(Color):
id_color name_color
1 blue
2 red
3 green
Table3(Variety):
id_variety id_color id_group name_variety
1 1 1 light
2 3 1 dark
3 6 2 dark
Table4(Tone):
id_tone id_color id_group name_tone
1 1 1 ocean
2 5 1 sea
3 9 3 clay
Given an id_group like 1 I want to make a selection resulting something like this:
id_group id_color name_variety name_tone
1 1 light ocean
1 3 dark NULL
1 5 NULL sea
I was able to solve the problem with an union and changing the order of the JOINS but I think that there must be another solution
SELECT
GRO.id_group, COL.id_color, VARI.name_variety, TONE.name_tone
FROM
groups GRO
LEFT OUTER JOIN
variety VARI ON (VARI.id_group = GRO.id_group)
LEFT OUTER JOIN
tone TONE ON (TONE.id_group = GRO.id_group)
AND (TONE.id_color = VARI.id_color)
LEFT OUTER JOIN
color COL ON (COL.id_color = VARI.id_color)
OR (COL.id_color = TONE.id_color)
WHERE
GRO.id_group = 1
UNION
SELECT
GRO.id_group, COL.id_color, VARI.name_variety, TONE.name_tone
FROM
groups GRO
LEFT OUTER JOIN
tone TONE ON (TONE.id_group = GRO.id_group)
LEFT OUTER JOIN
variety VARI ON (VARI.id_group = GRO.id_group)
AND (VARI .id_color = TONE.id_color)
LEFT OUTER JOIN
color COL ON (COL.id_color = VARI.id_color)
OR (COL.id_color = TONE.id_color)
WHERE
GRO.id_group = 1

Answer 1

I think what you want is something more like:
SELECT
id_group,
id_color,
MAX(max_variety),
MAX(max_tone)
FROM
(SELECT
v.id_group,
v.id_color,
MAX(name_variety) AS max_variety,
MAX(name_tone) AS max_tone
FROM
variety V INNER JOIN
color c ON
V.id_color = c.id_color LEFT OUTER JOIN
tone t ON
t.id_group = v.id_group AND
t.id_color = V.id_color
WHERE
v.id_group = 1
GROUP BY
v.id_group,
v.id_color
UNION ALL
SELECT
t.id_group,
t.id_color,
MAX(name_variety) AS max_variety,
MAX(name_tone) AS max_tone
FROM
tone t INNER JOIN
color c ON
t.id_color = c.id_color LEFT OUTER JOIN
variety V ON
v.id_group = t.id_group AND
v.id_color = t.id_color
WHERE
t.id_group = 1
GROUP BY
t.id_group,
t.id_color) u
GROUP BY
id_group,
id_color

Answer 2

instead of using union you could use full join , as full join return all result from first table and also all results from the second tables.
SELECT
GRO.id_group, COL.id_color, VARI.name_variety, Tone.name_tone from Variety VARI
join Color COL on col.id_color=VARI col.id
join Groups GRO on GRO.id_group=VARI.id_group
full join Tone on Tone.id_group=GRO.id_group
where GRO.id_group = 1