SQL Server Team-based Development - Red Gate Software

Client problems when reading data
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Chapter 11: SQL Refactoring
Use of SELECT * can cause duplicate column names to be returned in the result set, as
demonstrated in Listing 11-6. This will definitely cause client applications to throw an
exception when attempting to read columns by name. Always explicitly name the columns
to be returned and alias columns with the same names. If there are multiple columns
with the same name, then it might be a good idea to prefix the column names with a table
identifier, such as t1_name. However, this will change our output column names.
SELECT TOP 10
*
FROM master..spt_values t1
CROSS JOIN master..spt_values t2
- – same result set but with explicitly named columns
SELECT TOP 10
t1.name , t1.number , t1.type ,
t1.high , t1.low , t1.status ,
t2.name , t2.number , t2.type ,
t2.high , t2.low , t2.status
FROM master..spt_values t1
CROSS JOIN master..spt_values t2
Listing 11-6: Duplicate names due to use of SELECT *.
View refreshing problem
This is one of the trickier problems with SELECT *. If we use it in a view, and a column is
added to an underlying table, then this change isn't reflected in the view. We have to call a
stored procedure called sp_refreshview to refresh the schema returned by the view, so
our changes to the tables are seen. Listing 11-7 demonstrates this problem.