join – Sql multiple row based select like GraphQL

I have a large table i want to select different columns based on multiple conditions, rather than the entire column even if the row doesn’t need it.
something like :
i want (H1,H2) if HR1=R1 and (H2,H3) if H1=R2 …
problem is i can do a complete select to select all columns needed but that’s too much uneeded columns

select from ((select H2,H3 where H1=R1),(select H2,H4 where H1=R2), (select H5 where H1=R3))

after a certain number of the conditions in the query i get an empty result.

| H1 | H2 | H3  | H4  | H5  |
| R1 |[V1]|[V2] | V3  | V4  |
| R2 |[V5]| V6  |[V7] | V8  |
| R3 | V9 | V10 | V11 |[V12]|

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