Download OrderEntryQ37

[QueryID:37]
For each employee with a commission rate of less than 0.04, compute the number of
orders taken in January 2004. The result should include the employee number, the
employee last name, and the number of orders taken.
The following steps may be helpful in formulating the query for the
problem:
1. Mapping the data items required to the column names in the DB
employee number  EmpNo
employee last name  EmpLastName
number of orders taken by employees  COUNT(OrdNo)
2. Interpret the row selection condition
 Orders placed in January 2004  OrdDate is in January 2004  OrdDate >=
1-Jan-2004 and OrdDate <= 31-Jan2004 Alternatively OrdDate between 1Jan-2004 and 31-Jan-2004
 the order month is January and order year is
2004  date_part(month, OrdDate) = 1
and date_part(year, OrdDate) = 2004
 any dates in January 2004  OrdDate like
*-Jan-2004 (not recommended)
 Employee commission rate is less than 0.04  EmpCommRate < 0.04
3. Identify the table(s) needed, which contain(s) all the data items used in 1) and 2)
orderTbl table (M-table, FK)
employee table (1-table, PK)
4. How to join these tables
Joining condition — orderTbl.EmpNo =employee.EmpNo
Joining styles
– in FROM, orderTbl o join employee e on o.EmpNo = e.EmpNo or
-- in FROM, orderTbl o, employee e and in WHERE, o.EmpNo = e.EmpNo
-- in FROM, orderTbl o natural join employee e
or
5. Group result or individual result
An aggregate function COUNT() is used to calculate the number of orders taken by
each employee  group result, Group By is needed, the Grouping By column are
EmpNo, EmpLastName. Note the column EmpLastName is redundant but required by
SQL engine, and must be specified in Group By clasue as it appears in Select clause
and is not an aggregate column.
All groups are considered, no Having clause
6. Using the template:
SELECT <list of columns or expressions >
FROM <list of tables or join operations>
WHERE <row selection condition >
GROUP BY < list of grouping columns >
©H.Y Lu 2008