Question

The solution: https://stackoverflow.com/a/439768/857994 gives the following code:

    DELETE TableA 
    FROM TableA a
    INNER JOIN
    TableB b on b.Bid = a.Bid
    and [my filter condition]

My question is:

How come we don’t need an AS in the FROM to alias TableA to a here? Wouldn’t we need the AS in a select query like SELECT E.FirstName FROM Employee AS E;?

What’s the difference?

Answer 1

The “AS” keyword there is optional. You don’t need it in SELECT queries either. (Try it!)

Here’s some of the syntax of “FROM” from the MSDN:

[ FROM { <table_source> } [ ,...n ] ] 
<table_source> ::= 
{
    table_or_view_name [ [ AS ] table_alias ] [ <tablesample_clause> ] 
    ...
}

As you can see, the [ AS ] is in brackets, which means it’s optional. You never need to add it, though I suppose some may argue that it makes the query more readable. I disagree, but that’s a matter of personal preference (or your DBA’s personal preference).

See http://msdn.microsoft.com/en-us/library/ms177634.aspx for more detail.