Distinct only works on the entire row, regardless of where you place parentheses.

Your issue is cardinality of data. The fact that you have a table named T_ContactTypeContact indicates that a...

Here's an example of the impact, using temp tables, and just 10,000 rows. You can imagine what this scales to in your 800K sample. A SQL server data page is...

>>Why should a "long" column in the select list make this query so slow ?

Because a long nchar column drastically reduces the number of rows per data page, increases considerably...

Tested and working:

Select ListName

FROM #tblParent As p

Inner Join

(

  Select ParentID, Count(Distinct CategoryCode) As CountAB

  From #tblChild

  WHERE CategoryCode in ('A','B')

  Group By ParentID

) dt

  On p.ID = dt.ParentID

Where...

Select t1.ID, t1.Value,

  (Select Sum(t2.Value) From YourTable As t2

   Where t2.ID = t1.ID And t2.Identity <= t1.Identity 

   ) As Summed

From YourTable As t1

Is there a 3rd column available in the original 2 column set that supplies the order in which the rows occur ?

Update P

Set

  price = O.price

From Products As P

Inner Join Products_Options As OP

  On (OP.ProductID = P.ProductID)

Inner Join Options As O

  On (O.OptionID = OP.OptionID And

        O.ProductID = OP.ProductID)

>>1. What will the drawbacks of having no Clustered index on a table? (for both static & transactional table)

Table fragmentation. Maintenance utilities like DBCC DBREINDEX() will not be able to...

DECLARE @y INT

SELECT @y = COUNT(*)  FROM Customers

>>PW: is there any need for the following...

>>dt.MaxCreatedPerGroup = tbl1.DateCreated

It doesn't work without that. The purpose of the derived table is to find the most recent date per GroupID....

That "simple" query is too simple:

group by groupID, groupValue

You can't group on GroupValue, if the requirement is to eliminate all but 1 of the GroupValues for each...

Join to a derived table that gives you Max(Date) per group to join to:

select tbl1.groupID, tbl1.groupValue, tbl1.dateCreated

from tbl1

Inner Join

(

  Select GroupID, Max(DateCreated) As MaxCreatedPerGroup

  From tbl1

  Group By GroupID

) dt

 ...

Use derived tables instead of sub-queries

Use joins instead of IN() for improved efficiency

Use a UNION ALL for mutually exclusive resultsets, instead of an OR condition

select distinct customer_id

from orders As...

A DBCC DBREINDEX would probably be useful. If the tables that are pulled in are essentially readonly for reporting purposes, you could DBREINDEX with a 100% fillfactor, which would reduce...

Syntax error in my delete code.

DELETE ar

FROM @tblARData As ar

WHERE EXISTS (

  SELECT *

  FROM @tblARDataTemp As t

  WHERE t.Site = ar.Site

)