Joining three tables with intermediate nullable option and filter condition
Sorry if this seems like a dumb question, but I've read through tens of answers and tried many different options, yet my query results were either overly inclusive or exclusive.
The basic scenario is, having tables A <- B <- C, and the foreign keys A.b_id (nullable) and B.c_id, how can I get A's where either:
b_idis null (B is absent)
b_idis not null (B is present), AND its associated C fits a particular criterion (C.activeis true, or similar)
To restate, an A may be independent of a B, but every B belongs to a C, and I would like to get the A's that either have no B or have a B that belongs to a C with a specific condition.
Many answers seem to deal with an A that is joined to both B and C, but in this case it's the middle or intermediate table that is optional. (And I haven't been able to figure out how to assemble parts of different examples into a working solution.)
It may be possible through a UNION, but that also seems like a last resort. Is there a way to do this through joins?
I had tried inner joining B and C and then having A left join that as a derived (aliased) table, but this would still return all results, even where (using the example) active was false.
Thanks.
postgresql query
asked 6 mins ago
SexxLuthorSexxLuthor
1011
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Sorry if this seems like a dumb question, but I've read through tens of answers and tried many different options, yet my query results were either overly inclusive or exclusive.
The basic scenario is, having tables A <- B <- C, and the foreign keys A.b_id (nullable) and B.c_id, how can I get A's where either:
b_idis null (B is absent)
b_idis not null (B is present), AND its associated C fits a particular criterion (C.activeis true, or similar)
To restate, an A may be independent of a B, but every B belongs to a C, and I would like to get the A's that either have no B or have a B that belongs to a C with a specific condition.
Many answers seem to deal with an A that is joined to both B and C, but in this case it's the middle or intermediate table that is optional. (And I haven't been able to figure out how to assemble parts of different examples into a working solution.)
It may be possible through a UNION, but that also seems like a last resort. Is there a way to do this through joins?
I had tried inner joining B and C and then having A left join that as a derived (aliased) table, but this would still return all results, even where (using the example) active was false.
Thanks.
postgresql query
asked 6 mins ago
SexxLuthorSexxLuthor
1011
New contributor
SexxLuthor is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
Sorry if this seems like a dumb question, but I've read through tens of answers and tried many different options, yet my query results were either overly inclusive or exclusive.
The basic scenario is, having tables A <- B <- C, and the foreign keys A.b_id (nullable) and B.c_id, how can I get A's where either:
b_idis null (B is absent)
b_idis not null (B is present), AND its associated C fits a particular criterion (C.activeis true, or similar)
To restate, an A may be independent of a B, but every B belongs to a C, and I would like to get the A's that either have no B or have a B that belongs to a C with a specific condition.
Many answers seem to deal with an A that is joined to both B and C, but in this case it's the middle or intermediate table that is optional. (And I haven't been able to figure out how to assemble parts of different examples into a working solution.)
It may be possible through a UNION, but that also seems like a last resort. Is there a way to do this through joins?
I had tried inner joining B and C and then having A left join that as a derived (aliased) table, but this would still return all results, even where (using the example) active was false.
Thanks.
postgresql query
asked 6 mins ago
SexxLuthorSexxLuthor
1011
New contributor
SexxLuthor is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Sorry if this seems like a dumb question, but I've read through tens of answers and tried many different options, yet my query results were either overly inclusive or exclusive.
The basic scenario is, having tables A <- B <- C, and the foreign keys A.b_id (nullable) and B.c_id, how can I get A's where either:
b_idis null (B is absent)
b_idis not null (B is present), AND its associated C fits a particular criterion (C.activeis true, or similar)
To restate, an A may be independent of a B, but every B belongs to a C, and I would like to get the A's that either have no B or have a B that belongs to a C with a specific condition.
Many answers seem to deal with an A that is joined to both B and C, but in this case it's the middle or intermediate table that is optional. (And I haven't been able to figure out how to assemble parts of different examples into a working solution.)
It may be possible through a UNION, but that also seems like a last resort. Is there a way to do this through joins?
I had tried inner joining B and C and then having A left join that as a derived (aliased) table, but this would still return all results, even where (using the example) active was false.
Thanks.
postgresql query
postgresql query
asked 6 mins ago
SexxLuthorSexxLuthor
1011
New contributor
SexxLuthor is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 mins ago
SexxLuthorSexxLuthor
1011
New contributor
SexxLuthor is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 mins ago
SexxLuthorSexxLuthor
1011
New contributor
SexxLuthor is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 mins ago
SexxLuthorSexxLuthor
1011
asked 6 mins ago
SexxLuthorSexxLuthor
1011
1011
New contributor
SexxLuthor is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
SexxLuthor is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
SexxLuthor is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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