Use arithmetic operators in queries

CREATE TABLE cust (
       c_id        INTEGER,
       c_first     VARCHAR(20),
       c_last      VARCHAR(20),
       c_credit    DECIMAL(10, 2)
 );

CREATE TABLE ordr (
       o_id         INTEGER,
       o_ol_cnt     INTEGER,
       o_entry_d    DATE
 );

CREATE TABLE item (
       i_id           INTEGER,
       i_name       VARCHAR(20),
       i_price       DECIMAL(10, 2)
 );

INSERT INTO cust VALUES(101,'Ann','Smith',16.10);
INSERT INTO cust VALUES(102,'Madeleine','Johnson',23.00);
INSERT INTO cust VALUES(103,'Michael','Brown',9.05);
INSERT INTO ordr VALUES(102,400,'2020-01-23');
INSERT INTO ordr VALUES(103,600,'2020-03-10');
INSERT INTO ordr VALUES(105,300,'2020-09-18');
INSERT INTO ordr VALUES(105,100,'2020-07-01');
INSERT INTO item VALUES(103,'Apple','12.9');
INSERT INTO item VALUES(103,'Banana','10.2');
INSERT INTO item VALUES(105,'Pear','9.8');

obclient> SELECT t1.c_first, t1.c_last, t1.c_credit, t2.o_ol_cnt * t3.i_price item_sum_price, t2.o_entry_d, t3.i_name, t3.i_price
      FROM cust t1
      JOIN ordr t2 ON (t1.c_id=t2.o_id)
      JOIN item t3 ON (t2.o_id=t3.i_id)
      ORDER BY t1.c_id, t2.o_id;
+---------+--------+----------+----------------+------------+--------+---------+
| c_first | c_last | c_credit | item_sum_price | o_entry_d  | i_name | i_price |
+---------+--------+----------+----------------+------------+--------+---------+
| Michael | Brown  |     9.05 |        7740.00 | 2020-03-10 | Apple  |   12.90 |
| Michael | Brown  |     9.05 |        6120.00 | 2020-03-10 | Banana |   10.20 |
+---------+--------+----------+----------------+------------+--------+---------+
2 rows in set