How can I put with regex, schema name table, for query select?
Query doesn't have fixed size.
select * from t1 union select * from t2
select * from schema1.t1 union select * from schema1.t2
(1) If you are using it in a code, maybe you can do a search and replace at front end as Luk suggested.
(2) Alternatively, in your current session you can set default schema as
schema1 so your query would work without schema name. But it would depend on your database name.
Like in Oracle you can do
ALTER SESSION SET CURRENT_SCHEMA=schema1
select * from t1 would effectively mean
select * from schema1.t1.
You can search
how to set default schema in <your database> in google and you would get syntax for other databases as well.