SQL Server extra text after table name in SELECT - sql

Question

I found a SQL statement to the effect of:
SELECT * FROM Users x
My question is: what is x? I have never seen this before.
Thanks.

Answer 1

x is an Alias for the table Users.
Using Table Aliases
The readability of a SELECT statement can be improved by giving a
table an alias, also known as a correlation name or range variable. A
table alias can be assigned either with or without the AS keyword:
SELECT * FROM Users x
SELECT * FROM Users AS x

Answer 2

It's an alias. The AS keyword is optional and has been left out, but it is the same as:
SELECT * FROM Users AS x
This means you can (in some implementations of SQL, SQL Server being one of them, must) use x in the rest of the query to refer back to the table Users specified here. For example:
SELECT x.MyColumn
FROM Users x
WHERE x.AnotherColumn = 42
There are three general use cases for aliases:
Readability. For long table names or when the name will be used many times, it can improve readability. For example, imagine the following without the alias:
SELECT x.SomeColumn, x.SomeOtherColumn, x.AThirdColumn
FROM [my crAzy Table Name with spaces in it] x
WHERE x.AnotherColumn = 42
Disambiguation. Often used for self-joins, note the use of the same table twice. You must use an alias to differentiate the two instances of the Users table:
SELECT x.SomeColumn, COUNT(y.SomeColumn)
FROM Users x
INNER JOIN Users y ON x.SomeOtherColumn < y.SomeOtherColumn
GROUP BY x.SomeColumn
Sub-queries in a FROM or JOIN clause (also called derived tables) must have a name. This is done by specifying an alias:
SELECT x.SomeColumn
FROM
(
SELECT SomeColumn
FROM Users
) x

Answer 3

It's just an alias for Users, which can be used in the query.
Imagine :
you want to retrieve datas from 2 tables, with an Id column in both
if you wanna retrieve these Ids, you have to prefix the column name to avoid confusion.
With alias:
select t1.Id, t2.Id
from mytableWithAReallyComplicatedName t1
inner join mySecondtableWithAReallyComplicatedName t2 on t1.Id = t2.Id
Without alias
select mytableWithAReallyComplicatedName.Id, mySecondtableWithAReallyComplicatedName.Id
from mytableWithAReallyComplicatedName
inner join mySecondtableWithAReallyComplicatedName on mytableWithAReallyComplicatedName.Id = mySecondtableWithAReallyComplicatedName .Id
It the table names are long, the query might be fast less practical to read, with the second version.