The SELECT clause is often referred to as the SELECT list, because it lists the values to be returned in the query’s results.

The simplest form of a SELECT clause is the use of the asterisk character (*) to return all columns. When used in T-SQL queries, it is called a star. While SELECT * is suitable for a quick test, you should avoid using it in production work for the following reasons:

• Changes to the table that add or rearrange columns will be reflected in the query results, which may result in unexpected output for applications or reports that use the query.
• Returning data that is not needed can slow down your queries and cause performance issues if the source table contains a large number of rows.