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What is the difference between
select empName as EmployeeName from employees
versus
select EmployeeName = empName from employees
from a technical point of view. Not sure if this is just SQL server specific or not.
Appreciate your answers.
469
The basic syntax of a table alias is as follows. SELECT column1, column2.... FROM table_name AS alias_name WHERE [condition];
A column alias is a temporary, alternate name for a column. Aliases are specified in the SELECT clause to name or rename columns so that the result table is clearer or easier to read. Aliases are often used to name a column that is the result of an arithmetic expression or summary function. An alias is one word only.
SQL aliases are used to give a table, or a column in a table, a temporary name. Aliases are often used to make column names more readable. An alias only exists for the duration of that query.
SQL Server column alias To assign a column or an expression a temporary name during the query execution, you use a column alias. In this syntax, you use the AS keyword to separate the column name or expression and the alias.
I'd prefer the first one, since the second one is not portable -
select EmployeeName = empName from employees
is either a syntax error (at least in SQLite and Oracle), or it might not give you what you expect (comparing two columns EmployeeName and empName and returning the comparison result as a boolean/integer), whereas
select empName EmployeeName from employees
is the same as
select empName as EmployeeName from employees
which is my preferred variant.
65
The main advantage of the second syntax is that it allows the column aliases to be all lined up which can be of benefit for long expressions.
SELECT foo,
bar,
baz = ROW_NUMBER() OVER (PARTITION BY foo ORDER BY bar)
FROM T
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