Add automatic type cast for integer literals

In parameterized statements integer literals, like Int(num), are replaced with a placeholders. For some expressions,
postgres interpreter will not have enough information to deduce the type. If this is the case postgres returns an error.
Int8, Int16, Int32.... functions now will add automatic type cast over a placeholder, so type deduction is always possible.

tests/postgres/select_test.go

@@ -1943,7 +1943,7 @@ SELECT customer.customer_id AS "customer.customer_id",
      customer.last_update AS "customer.last_update",
      customer.active AS "customer.active"
 FROM dvds.customer
-WHERE ($1 AND (customer.customer_id = $2)) AND (customer.activebool = $3);
+WHERE ($1::boolean AND (customer.customer_id = $2)) AND (customer.activebool = $3::boolean);
 `, true, int64(1), true)
 
 	dest := []model.Customer{}
@@ -2403,3 +2403,24 @@ func TestRecursionScanNx1(t *testing.T) {
 `)
 	})
 }
+
+// In parameterized statements integer literals, like Int(num), are replaced with a placeholders. For some expressions,
+// postgres interpreter will not have enough information to deduce the type. If this is the case postgres returns an error.
+// Int8, Int16, .... functions will add automatic type cast over placeholder, so type deduction is always possible.
+func TestLiteralTypeDeduction(t *testing.T) {
+	stmt := SELECT(
+		SUM(
+			CASE().WHEN(Staff.Active.IS_TRUE()).
+				THEN(Int8(6)).   // if Int8 and Int32 are replaced with Int,
+				ELSE(Int32(-1)), // execution of this statement will return an error
+		).AS("num_passed"),
+	).FROM(Staff)
+
+	testutils.AssertStatementSql(t, stmt, `
+SELECT SUM((CASE WHEN staff.active IS TRUE THEN $1::smallint ELSE $2::integer END)) AS "num_passed"
+FROM dvds.staff;
+`)
+
+	err := stmt.Query(db, &struct{}{})
+	require.NoError(t, err)
+}