我需要显示每个'id'有多少不同的值.
它应该如下所示:
id | component_a | component_b | component_c
--------------------------------------------------
KLS11 | none | one | none
KLS12 | one | one | none
KLS13 | several | one | none
KLS14 | one | one | one
KLS15 | one | several | several
我有下表(table_a):
id | component_a | component_b | component_c
--------------------------------------------------
KLS11 | | a |
KLS12 | a | a |
KLS13 | a | a |
KLS13 | b | a |
KLS14 | a …