Sams Teach Yourself Transact-SQL in 21 Days, Second Edition

Day 4

Quiz

1:	Put the following keywords in order to make a SELECT statement work properly: GROUP BY HAVING SELECT DISTINCT WHERE FROM ORDER BY ROLLUP
A1:	Answer: SELECT DISTINCT FROM WHERE GROUP BY ROLLUP HAVING ORDER BY
2:	What is the difference between COUNT(*) and COUNT(expression)?
A2:	COUNT(expression) evaluates the expression in each row. Only non-null values are counted. COUNT(*) counts every row. It does not examine any columns.
3:	Is the following query permitted? If not, how would you correct it? select ProductID, ProductName from Products where UnitPrice > avg(UnitPrice)
A3:	The query is not permitted. An aggregate function (AVG) cannot appear in a WHERE clause unless it is part of a subquery. Here is the corrected query: select ProductID, ProductName ...