sql - postgresql insert or create with temp table merge -

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i have 3 tables: a b , c. b temp table created output of csv. goal copy necessary values b a but 1 of attributes has created or selected c.

so far have

with table_c_data (   insert table_c (id)   select table_c_id   table_b b         not exists (select * table_c c b.table_c_id = c.id)   returning * )  insert table_a (w,x,y,z) select table_c.id, x, y, z table_b inner join table_c_data table_c on table_b.table_c_id = table_c.id;

but having trouble figuring out how have original table_c_data return if record does existing. (before added in where clause specifying existing query ran expected, trying handle uniquness constraints have check whether record exists first)


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