选择同一表中的行数

Question

Hi I have a table as below and I need to select the count of different trade IDs for given distinct OrderIds I am unable to do so in MySQL format

+-----------+---------+
| OrderID   |TradeID  |
+===========+=========+
| 1         | 58761   |
+-----------+---------+
| 1         | 58762   | 
+-----------+---------+
| 2         | 58763   | 
+-----------+---------+
| 2         | 58764   | 
+-----------+---------+
| 2         | 58765   |
+-----------+---------+

Where result is required as

+-----------+---------+
| OrderID   |Count    |
+===========+=========+
| 1         | 2       |
+-----------+---------+
| 2         | 4       | 
+-----------+---------+

Answer 1

Just COUNT / GROUP BY

SELECT OrderID, COUNT(*) 
FROM some_table 
GROUP BY OrderID

SQL Fiddle here:-

http://www.sqlfiddle.com/#!9/305630/1

Note that if you wanted a couple of distinct TradeIDs for each OrderID you could use

SELECT OrderID, COUNT(DISTINCT TradeID) 
FROM some_table 
GROUP BY OrderID