The extended aggregate

After you execute the CREATE FUNCTION statement in Registering the overloaded plus() function , you can use the SUM aggregate on complexnum_t columns. For example, suppose you create the tab1 table as the following code fragment shows.
Figure 1: A table with a complexnum_t column
CREATE TABLE tab1
   (col1 INTEGER,
   col2 complexnum_t,
   col3 INTEGER);

INSERT INTO tab1 
   VALUES (1, row(1.5, 3.7)::complexnum_t, 24);
INSERT INTO tab1 
   VALUES (2, row(6.9, 2.3)::complexnum_t, 13);
INSERT INTO tab1 
   VALUES (3, row(4.2, 9.4)::complexnum_t, 9);
INSERT INTO tab1 
   VALUES (4, row(7.0, 8.5)::complexnum_t, 5);
INSERT INTO tab1 
   VALUES (5, row(5.1, 6.2)::complexnum_t, 31);
INSERT INTO tab1 
   VALUES (6, row(3.9, 4.6)::complexnum_t, 19);
The following query uses the SUM aggregate function on the complexnum_t column, col2: 
SELECT SUM(col2) FROM tab1;
With the rows that A table with a complexnum_t column has inserted, the preceding query yields a complexnum_t value of: 
ROW(28.6, 34.7)
As a side effect of the new plus() function, you can also add two complexnum_t columns in an SQL expression, as follows: 
SELECT complex_num1 + complex_num2 FROM complex_nums
WHERE id > 6;