Sql server® 2012 t-sql fundamentals

 

CHAPTER 3

 

Joins

 

 101

Employees.empid). The purpose of the prefixes is to facilitate the identification of columns in an un-

ambiguous manner when the same column name appears in both tables. The aliases of the tables are 

assigned for brevity. Note that you are required to use column prefixes only when referring to am-

biguous column names (column names that appear in more than one table); in unambiguous cases, 

column prefixes are optional. However, some people find it a good practice to always use column 

prefixes for the sake of clarity. Also note that if you assign an alias to a table, it is invalid to use the full 

table name as a column prefix; in ambiguous cases you have to use the table alias as a prefix.