SQL Tips and Tricks

When writing SQL it is possible to use ORDER BY with CASE conditions to help provide more flexibility over the returned order of a record set and this is especially useful when writing stored procedures which require a dynamic ORDER BY clause. This method does not require any dynamic SQL build up strings executed either using EXEC or sp_executeSQL

Lets take this example using the AdventureWorks database that is downloadable for SQL Server.

This procedure which is designed to accept three parameters which will help return records for a sales person  and in a specified column order and in a particular sort order.

CREATE PROCEDURE usp_GetOrders @SalesPersonID INT, @OrderBy VARCHAR(20), @SortOrder CHAR(4)
AS
SELECT SalesOrderNumber, PurchaseOrderNumber, TotalDue, OrderDate, DueDate, AccountNumber  
FROM Sales.SalesOrderHeader
WHERE SalesPersonID = @SalesPersonID
ORDER BY 
  CASE WHEN @OrderBy = 'Due Date' AND @SortOrder = 'DESC' THEN DueDate END DESC,
  CASE WHEN @OrderBy = 'Due Date' THEN DueDate END,
  CASE WHEN @OrderBy = 'Order Date' AND @SortOrder = 'DESC' THEN OrderDate END DESC,
  CASE WHEN @OrderBy = 'Order Date' THEN OrderDate END,
  CASE WHEN @OrderBy = 'Total Due' AND @SortOrder = 'DESC' THEN TotalDue END DESC,
  CASE WHEN @OrderBy = 'Total Due' THEN TotalDue END

One thing you might notice, I have supplied the DESC version of the CASE first for each column. There are two reasons for this; the default sort order if often ASC so I have not supplied an ASC for second CASE for each column but in doing this (the second reason), the CASE will not work correctly if the DESC is the second line as the first line will always return true.

So this:

CASE WHEN @OrderBy = 'Due Date' THEN DueDate END,  
CASE WHEN @OrderBy = 'Due Date' AND @SortOrder = 'DESC' THEN DueDate END DESC,

Will always return the data in ASC order regardless of whether I supply DESC in @SortOrder. In this case either make DESC the first line as written or re-write as:

CASE WHEN @OrderBy = 'Due Date' AND @SortOrder = 'ASC' THEN DueDate END,  
CASE WHEN @OrderBy = 'Due Date' AND @SortOrder = 'DESC' THEN DueDate END DESC,

I hope you found this useful. If you know of better ways to achieve this, please leave a comment. I’d love to hear from you! 🙂

I’ve used SELECT TOP (x) many, many times. After learning how to use SELECT, it’s something I quickly learned to use and remains something which I continue to use often.

I’ve also used TOP (x) with UPDATE and DELETE statements to limit the number of rows updated or deleted in a statement. I’ve never had to use SELECT TOP WITH TIES though.

I’ve glanced through the documentation in the past and thought – “must learn that one day” but never had the time or need to. I guess some things you learn how to use only when you have to.

So this post is dedicated to my learning experience of using SELECT TOP WITH TIES 🙂

What does SELECT TOP WITH TIES do?

Let’s take an example. Say you wanted to retrieve the first 5 rows from a table and you ordered by a specific column. So you get back 10 rows ordered by your column.

Now apply SELECT TOP (5) WITH TIES and any row which has a column value that matches the last row’s column value as defined by the ORDER BY clause will also be returned in the results. So you get more rows than what is specified in TOP (x).

Let’s do an example 🙂

CREATE TABLE FamousTransformers
(ID SMALLINT PRIMARY KEY IDENTITY(1,1),
FirstName VARCHAR(100) NOT NULL,
LastName VARCHAR(100) NOT NULL,
FavouriteColour VARCHAR(50) NOT NULL);

--populate with some data (6 rows to demonstrate this working)
INSERT INTO FamousTransformers(FirstName, LastName, FavouriteColour)
VALUES('Clark','Kent','Blue');
INSERT INTO FamousTransformers(FirstName, LastName, FavouriteColour)
VALUES('Bruce','Wayne','Black');
INSERT INTO FamousTransformers(FirstName, LastName, FavouriteColour)
VALUES('Peter','Parker','Red');
INSERT INTO FamousTransformers(FirstName, LastName, FavouriteColour)
VALUES('Optimus','Prime','Red');
INSERT INTO FamousTransformers(FirstName, LastName, FavouriteColour)
VALUES('David','Banner','Green');
INSERT INTO FamousTransformers(FirstName, LastName, FavouriteColour)
VALUES('Rodimus','Prime','Orange');

--select using normal TOP(x)

SELECT TOP (5) FirstName, LastName, FavouriteColour
FROM FamousTransformers
ORDER BY FavouriteColour

Returns….

FirstName            LastName             FavouriteColour
-------------------- -------------------- --------------------
Bruce                Wayne                Black
Clark                Kent                 Blue
David                Banner               Green
Rodimus              Prime                Orange
Optimus              Prime                Red

(5 row(s) affected)

--now execute using WITH TIES
SELECT TOP (5) WITH TIES FirstName, LastName, FavouriteColour
FROM FamousTransformers
ORDER BY FavouriteColour

FirstName            LastName             FavouriteColour
-------------------- -------------------- --------------------
Bruce                Wayne                Black
Clark                Kent                 Blue
David                Banner               Green
Rodimus              Prime                Orange
Peter                Parker               Red
Optimus              Prime                Red

(6 row(s) affected)

So you can see the extra row appearing there where “Optimus Prime” is displayed because he has the same favourite colour as “Peter Parker”. The FavouriteColour column is the key here as defined in the ORDER BY statement.

Actual use cases for SELECT TOP WITH TIES

I can think of one straight off the top of my head. If you had a league table of top performing sales people and wanted to bring back the top three performers, what if two sales people were tied for 3rd and 4th place on revenue? No way to differentiate them, they should both be returned in the results and share 3rd place.

And finally….

You must use ORDER BY and TOP clauses together if you want to use WITH TIES.

I would typically use Management Studio to rename columns or tables in SQL Server. Afterall, it is an easy thing to do to open up the GUI make your changes and then save them back to the SQL Server.

Have you ever been in a situation where you wanted to make a number of such changes and then later on you needed to repeat those changes on another system?

I was in such a situation recently where due to some application changes, many columns had to be renamed, the application tested and then I had to repeat the procedure on production.

I did not want to have to open up every table in Management Studio and click the save button each time all over again!

I needed something that I could execute quickly, so I prepared a file of T-SQL commands to make my changes in one swift stroke. I achieved it all using sp_rename

T-SQL example – renaming columns and tables

So here we have an example for renaming a column:

EXEC sp_rename 'Table.[OldColumnName]', '[NewColumnName]', '[COLUMN]';

If we wanted to rename a table then we can use:

EXEC sp_rename '[OldTableName]', '[NewTableName]';

Note that the square brackets are not mandatory but are necessary when you have silly database designers who have put such things as hyphens or spaces in their field names. Makes me cringe just thinking about it! 😐

Permissions needed for sp_rename

You need ALTER permission if you want to rename tables or columns.

One final note

You can use sp_rename for renaming other objects besides tables. It can also be used for renaming indexes, constraints, types databases and statistics. More more information on this useful little proc, visit this link