Solved

TSQL - Order of evaluation

Posted on 2009-06-30
3
715 Views
Last Modified: 2012-05-07
Hi

I am quite new to SQL and want to confirm check how the order of evaluation works for the below statement. I want to ensure it pulls the right data. It involves four tables tblEmployee, tblBookingActual, tblBookingRequested and tlkpCostCentre.

I understand that AND statements take priority over OR statements. But how can you ensure AND statements are evaluated in the correct order? Is it simple the order  they are placed in the SQL statement and the how you place the Parentheses ( )?
SELECT     dbo.tlkpCostCentre.Grouping, dbo.tlkpCostCentre.Area, dbo.tblBookingActual.CostCentre, dbo.tblBookingActual.PayrollNo, 

                      COUNT(dbo.tblBookingActual.BookingRef) AS [Number of Bookings for UnQualified], @StartDate AS StartDate, @EndDate AS EndDate

FROM         dbo.tblEmployee INNER JOIN

                      dbo.tblBookingActual ON dbo.tblEmployee.PayrollNo = dbo.tblBookingActual.PayrollNo INNER JOIN

                      dbo.tlkpCostCentre ON dbo.tblBookingActual.CostCentre = dbo.tlkpCostCentre.CostCentre INNER JOIN

                      dbo.tblBookingRequested ON dbo.tblBookingActual.BookingRef = dbo.tblBookingRequested.BookingRef

WHERE     (dbo.tblBookingActual.PayrollNo = 'NON02') AND (dbo.tblBookingRequested.RequiredDate BETWEEN @StartDate AND @EndDate) AND 

                      (dbo.tblEmployee.Grade IN ('BAND 5', 'BAND 5 / 5', 'BAND 6', 'BAND 6 / 6', 'BAND 7', 'BAND 7 / G', 'BAND 8', 'D', 'E', 'F', 'G', 'H'))

GROUP BY dbo.tlkpCostCentre.Grouping, dbo.tlkpCostCentre.Area, dbo.tblBookingActual.CostCentre, dbo.tblBookingActual.PayrollNo

ORDER BY dbo.tlkpCostCentre.Grouping, dbo.tlkpCostCentre.Area, dbo.tblBookingActual.CostCentre

Open in new window

0
Comment
Question by:adypips
  • 2
3 Comments
 
LVL 31

Assisted Solution

by:RiteshShah
RiteshShah earned 250 total points
ID: 24743774
"And" gets priority on "OR", if you have multiple "AND"s than it will go on left to right basis but be informed that parenthases always gets highest priority.
0
 
LVL 31

Assisted Solution

by:RiteshShah
RiteshShah earned 250 total points
ID: 24743786
0
 
LVL 57

Accepted Solution

by:
Raja Jegan R earned 250 total points
ID: 24743808
To find out how your query works exactly in your environment, you have to view the explain plan of the query:

In SSMS, Right click your Query Execution Pane and Click on Include Actual Execution plan and execute the query now.

Execution plan created will clearly display how your query is executed.

As far as your operator precedence doubt is cleared already.
0

Featured Post

3 Use Cases for Connected Systems

Our Dev teams are like yours. They’re continually cranking out code for new features/bugs fixes, testing, deploying, testing some more, responding to production monitoring events and more. It’s complex. So, we thought you’d like to see what’s working for us.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

I'm trying, I really am. But I've seen so many wrong approaches involving date(time) boundaries I despair about my inability to explain it. I've seen quite a few recently that define a non-leap year as 364 days, or 366 days and the list goes on. …
Slowly Changing Dimension Transformation component in data task flow is very useful for us to manage and control how data changes in SSIS.
Via a live example, show how to extract information from SQL Server on Database, Connection and Server properties
Viewers will learn how to use the INSERT statement to insert data into their tables. It will also introduce the NULL statement, to show them what happens when no value is giving for any given column.

920 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

18 Experts available now in Live!

Get 1:1 Help Now