Postgres SQL SELECT data from the table the entry exists with ID

Question

I have the following scenario.I have 3 tables with the following structure.

TABLE A
 -entry_id (PRIMARY KEY, INTEGER)

TABLE B 
 -entry_id (FOREIGN_KEY -> TABLE A)
 -content (TEXT)

TABLE C
  -entry_id (FOREIGN_KEY -> TABLE A)
  -content (INTEGER)

I want to retrive the content cell value from either table B or table C. The value can be in just one of the table. So it is either table B or C witch have an entry with a given entry_id.

PS. Sorry if duplicate did not manage to find anything to match what i need.

Would like something that works with also a 4th table. For example: TABLE D -entry_id (FOREIGN_KEY -> TABLE A) -content (DOUBLE) — Cosmin_Victor
– Cosmin_Victor, Commented Jun 20, 2017 at 9:37

Oto Shavadze · Accepted Answer · 2017-06-20 09:50:57Z

1

If I correctly understand, you need something like:

select entry_id, content::text from TABLEB where entry_id = ?
union all
select entry_id, content::text from TABLEC where entry_id = ?
union all
select entry_id, content::text from TABLED where entry_id = ?

edited Jun 20, 2017 at 9:50

answered Jun 20, 2017 at 9:38

Oto Shavadze

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2 Comments

Cosmin_Victor Over a year ago

No my problem is that i have an entry_id and the value for that entry_id can be in any of the 3 tables(a value can only be in one table for and entry_id).So i want based on the entry_id to retrive the corespondent data from one of the other 3 tables.Does it make sense?

Oto Shavadze Over a year ago

@Cosmin_Victor - then add where clause to all query, please check edited answer.

JohnHC · Accepted Answer · 2017-06-20 09:48:12Z

1

If it can only exist in one table at a time, use a union

select a1.entry_id, b2.content
from TableA a1
inner join TableB b2
on a1.entry_id = b2.entry_id

union -- This removes any duplicates. Use UNION ALL to show duplicates

select a1.entry_id, c3.content::text
from TableA a1
inner join TableC c3
on a1.entry_id = c3.entry_id

edited Jun 20, 2017 at 9:48

answered Jun 20, 2017 at 9:10

JohnHC

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2 Comments

Vao Tsun Over a year ago

UNION will remove duplicates, why you predicate "only exist in one table at a time"?..

Cosmin_Victor Over a year ago

1) UNION types integer and text cannot be matched.

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