What does syntax like "v.*" mean in MySQL Query?

Question

I have the following PHP code, with MySQL code that I'm having trouble understanding:

$result = $conn->query("SELECT v.*, (select count(*) from $table2 where ParentSyncGuid=v.SyncGuid) children FROM $table2 v WHERE v.ParentSyncGuid IS NULL OR v.ParentSyncGuid = ''");

The $table2 is defined earlier as the correct MySQL table.

However, "v" is not the name of any variable, table, or anything I can understand -- can someone explain the above query? The table being queried has entries where there are a few "root" entries, and every other entry has a parent that eventually links back to the root entries, hence the parent/id syntax, and the above code is meant to find just the root elements from my understanding... but I cannot get it to work and have never seen the "v." syntax before, and cannot find any documentation on it.

Answer 1

In the SQL there is this string: FROM $table2 v
The table can be access now with the alias name v

You could use * for selecting all available columns from all joined tables
v.* uses only the columns from table v

Example: Given are the following tables:
TableA with the columns a1 and a2
TableB with the columns a1 and b2

SELECT * FROM TableA JOIN TableB ON (...)

This would give an result set with all 4 columns

SELECT TableA.* FROM  TableA JOIN TableB ON (...)

This would give an result set only with the columns a1 and a2

SELECT v.* FROM  TableA v JOIN TableB ON (...)

This is exactly the same as above, but with alias names

See also: http://www.w3schools.com/sql/sql_alias.asp

Answer 2

See the "From $table2 v" portion of the SQL statement. That gives the table the alternative name v. This is called an alias.

If it was written fully it would be "From $table2 AS v"

The AS keyword is optional and so is often omitted.