A SELECT clause is not a list of columns, it is a list of expressions (which usually involve columns). A type cast is an expression so you can put them right into your SELECT. PostgreSQL supports two casting syntaxes:
CAST ( expression AS type )
expression::type
The first is standard SQL, the ::
form is PostgreSQL-specific. If your schb.customer.col3
is (for example) numeric(5,2)
, then you'd say:
INSERT INTO schb.customer (col1, col2, col3)
SELECT col1, col2, cast(col3 as numeric(5,2))
FROM scha.customer
-- or
INSERT INTO schb.customer (col1, col2, col3)
SELECT col1, col2, col3::numeric(5,2)
FROM scha.customer
Note that I've included the column list in the INSERT as well. You don't have to do that but it is a good idea as you don't have to worry about the column order and it makes it easy to skip columns (or let columns assume their default values with explicitly telling them to).