Question

I am trying to run a query using JOIN.
so, I wrote the below:

SELECT * FROM (SELECT trade_date, trade_time, price, contract_name 
               FROM test 
               WHERE contract_name="Z10" 
               AND trade_date="2010-12-01" 
               AND trade_time="0900") 
AS A JOIN (SELECT trade_date, trade_time, price, contract_name 
           FROM test 
           WHERE contract_name="H11" 
           AND trade_date="2010-12-01" 
           AND trade_time="0900") 
AS B ON (A.trade_date=B.trade_date 
AND A.trade_time=B.trade_time);

it runs fine, except it returns a large number of rows:

+------------+------------+-------------+---------------+------------+------------+-------------+---------------+
172025 rows in set (0.31 sec)

so I ran the below 2 queries individually to check how many max rows I should get, and from the below it should not exceed 1000.

mysql> select count(*) 
       from test 
       where contract_name="Z10" 
       and trade_date="2010-12-01" 
       and trade_time="0900";
+----------+
| count(*) |
+----------+
| 983 |
+----------+
1 row in set (0.02 sec)

mysql> select count(*) 
       from test 
       where contract_name="H11" 
       and trade_date="2010-12-01" 
       and trade_time="0900";
+----------+
| count(*) |
+----------+
| 175 |
+----------+

Can anyone suggest how I edit my JOIN to get the union of the 2 contracts on the selected date and time.

Answer 1

You in fact don’t need to do the join if you are getting result from same table. You can do this:

select count(*)
from test
where contract_name in ("H11","z10")
  and trade_date="2010-12-01"
  and trade_time="0900";