Question

I’m trying to learn advanced sql and how to use system queries (sql server). The below query is a little confusing.

CREATE PROC dbo.ShowHierarchy (     @Root int ) AS BEGIN     SET NOCOUNT ON     DECLARE @EmpID int, @EmpName varchar(30)      SET @EmpName = (SELECT EmpName FROM dbo.Emp WHERE EmpID = @Root)     PRINT REPLICATE('-', @@NESTLEVEL * 4) + @EmpName      SET @EmpID = (SELECT MIN(EmpID) FROM dbo.Emp WHERE MgrID = @Root)      WHILE @EmpID IS NOT NULL     BEGIN         EXEC dbo.ShowHierarchy @EmpID         SET @EmpID = (SELECT MIN(EmpID) FROM dbo.Emp WHERE MgrID = @Root AND EmpID > @EmpID)     END END GO 

Taken from here:

http://vyaskn.tripod.com/hierarchies_in_sql_server_databases.htm

Every time the query runs, how is the @EmpId parameter incremented? Does it do itself? Also, does the @root increment on every recursion? E.g. CEO is root, go to immediate subordinate, that immediate subordinate is now @root, etc.

Thanks

Answer 1

Every time the query runs, how is the @EmpId parameter incremented? Does it do itself?

This one:

SET @EmpID = (SELECT MIN(EmpID) FROM dbo.Emp WHERE MgrID = @Root AND EmpID > @EmpID) 

selects minimal EmpID that is greater than the one already selected, and assigns it to the @EmpID.

Of course, if there are any, new @EmpID will be greater than the old one, which means that @EmpID is incremented.