Obtain Union all result in ActiveRecord - ruby-on-rails

Question

Hows do one obtain the UNION operation result in Rails.
Given I have the following SQL statement
SELECT "sip_trunks".* FROM "sip_trunks" WHERE "sip_trunks"."default" = t LIMIT 1 UNION ALL SELECT "sip_trunks".* FROM "sip_trunks" WHERE "sip_trunks"."default" = f LIMIT 1
Thus far I have managed to construct the SQL using AREL with union all statement.
SipTrunk.where(default: true).limit(1).union(:all,SipTrunk.where(default: false).limit(1))
But attempting to query this result and AREL i.e Arel::Nodes::UnionAll and I'm unable to obtain the DB result.
Also running to_sql on the statement yield a SQL like this..
( SELECT "sip_trunks".* FROM "sip_trunks" WHERE "sip_trunks"."default" = $1 LIMIT 1 UNION ALL SELECT "sip_trunks".* FROM "sip_trunks" WHERE "sip_trunks"."default" = $2 LIMIT 1 )
this seem like a prepared statement but I don't see any prepared statement in DB
Attempting to use the above SQL using find_by_sql
SipTrunk.find_by_sql(SipTrunk.where(default: true).limit(1).union(:all,SipTrunk.where(default: false).limit(1)).to_sql,[['default',true],['default',false]])
with following error
ActiveRecord::StatementInvalid: PG::SyntaxError: ERROR: syntax error at or near "UNION"
LINE 1: ...trunks" WHERE "sip_trunks"."default" = $1 LIMIT 1 UNION ALL ...
How do I get the final SQL rows, from here?

Answer 1

Here is how I would perform this operation.
sql1 = SipTrunk.where(default: true).limit(1).arel
sql2 = SipTrunk.where(default: false).limit(1).arel
subquery = Arel::Nodes::As.new(
Arel::Nodes::UnionAll.new(sql1,sql2),
SipTrunk.arel_table
)
SipTrunk.from(subquery)
This will result in the following SQL
SELECT
sip_trunks.*
FROM
( SELECT
sip_trunks.*
FROM
sip_trunks
WHERE
sip_trunks.default = t
LIMIT 1
UNION ALL
SELECT
sip_trunks.*
FROM
sip_trunks
WHERE
sip_trunks.default = f
LIMIT 1) AS sip_trunks
And this will return an ActiveRecord::Relation of SipTrunk objects.

Answer 2

You can do a union like this, concatenating the two sql queries.
sql1 = SipTrunk.where(default: true).limit(1).to_sql
sql2 = SipTrunk.where(default: false).limit(1).to_sql
#sip_trunks = SipTrunk.find_by_sql("(#{sql1}) UNION (#{sql2})")
If you want to be fancy or have more than one sql queries to join you can to this
final_sql = [sql1, sql2].join(' UNION ')
#sip_trunks = SipTrunk.find_by_sql(final_sql)