Query across schemas in PostgreSQL
A construct like the following should work for you:

select *
from (
  select *
  from schemaA.tableA
  union all
  select *
  from schemaB.tableB
  union all
  ...
)
where columnA = "value";


You'll have to check the execution plans to see if the optimizer is smart enough to push the where clause into the subquery for each table.



The other thing to remember is that you can generate your queries by querying the metadata for a list of schema and table names.