How easy or difficult to write dynamic SQL ? TIP#110

This is one of the challenge for most of the developer to write dynamic SQL. Generally we follow the approach of string concatenation.

This seems very easy but we need to cast the  parameters in VARCHAR and sometimes we stuck in single code.

I am sure this happened with all of us. 

Let’s understand first a straight forward way which we (most of  us) are  using.

In example I am using person table of Adventureworks database and it is just a simple query  which provide person row according to primary key.

Now the above query is OK but it can be write in much better way with one of the SQL server in build stored procedure which is sp_executeSQL. This is one of the best way which have certain advantage which will discuss in next tip. Now see how we can write above query in much better way

DECLARE @BusinessEntityID   INT
DECLARE @DynamicSQL NVARCHAR(200)
DECLARE @Parameters NVARCHAR(100)

SET @BusinessEntityID = 1
SET @Parameters =N'@ParameterBusinessEntityID INT'

SET @DynamicSQL = N'SELECT * FROM [Person].[Person] WHERE BusinessEntityId = @ParameterBusinessEntityID '
EXECUTE sp_executesql @DynamicSQL, @Parameters,  @ParameterBusinessEntityID =@BusinessEntityID

If you see above query, you will find we are not using any type conversion the statement is clear without any type casting.

This is one of the best way to write dynamic query which is not only increase your statement’s readability but also increase performance of your query with certain amount.

Which we will discuss in next tip.

I hope now you are eager to use this and replace all your old fashion dynamic queries.

Please do post your feedback.

Enjoy !!!

RJ !!!

An interesting setting for NULL but don’t use it for future TIP #109

As we discussed earlier in TIP#103 for NULL in which I shared that we have to take extra care for NULL.

Now in this tip I would like to share one of the interesting setting for NULL. Although it is just for knowledge but don’t use it because it is deprecated in future version and by default you this setting is always on.

Still you are thinking for which setting I am talking about.

So , I am talking about “CONCAT_NULL_YIELDS_NULL”  . Let’s understand it by following example . By Default CONCAT_NULL_YIELDS_NULL is ON which means if anything added to NULL will be null as discussed earlier in our tip #103

Now, see what happens when we do it OFF.

So, We clearly saw in above image  when we set the CONCATE_NULL_YIELDS_NULL property to OFF it dissolved the NULL property.

My take on this property is that we should avoid it don’t try to make it OFF explicitly because if we do this then we explicitly breaking some hidden business rules.

I hope you will like this post.

Enjoy !!!

RJ !!

A big issue when try to Alter user define table type structure TIP #108

 

I hope all of you aware of  User define table type (a table value parameter) which we discussed earlier in TIP #57.

Now recently one interesting incident happened. We are using a user define table type in few stored procedure and due to some business requirement change we need to change /update data type of a particular column from TINYINT to SMALLINT.

Now this change was seems very simple you just need to change a column’s data type  but when you are going to do this, you will find this is not pretty straight forward (if the User define table type is referred in different tables).

If you go through standard steps you need to follow below steps (for  a column data type change)

1) Create a new User define table  type

2) Replaced old User define table  type with new user define table type in each stored procedures

3) Remove old User define table type.

And , I would like to say a big thanks  Mr.Norlado  who post an alternative on stackoverflow

below is the alternative steps

1) Rename the existing table type with following command

EXEC sys.sp_rename 'dbo.StudentTableType', 'zStudentTableType';

2) Create Table type with your  changes which you want

CREATE TYPE dbo.StudentTableType AS TABLE(
    StudentId INT NOT NULL,
    Name VARCHAR(255) NOT NULL,
    ClassId SMALLINT -- changed from tinyInt to smallint
);
3. Update the reference in sql entities

DECLARE @Name NVARCHAR(776);

DECLARE REF_CURSOR CURSOR FOR
SELECT referencing_schema_name + '.' + referencing_entity_name
FROM sys.dm_sql_referencing_entities('dbo.StudentTableType', 'TYPE');

OPEN REF_CURSOR;

FETCH NEXT FROM REF_CURSOR INTO @Name;
WHILE (@@FETCH_STATUS = 0)
BEGIN
    EXEC sys.sp_refreshsqlmodule @name = @Name;
    FETCH NEXT FROM REF_CURSOR INTO @Name;
END;

CLOSE REF_CURSOR;
DEALLOCATE REF_CURSOR;

4. Now drop the renamed table type

DROP TYPE dbo.zStudentTableType;

This 4 steps helped me a lot.

I hope this may help you as well.

Enjoy!!!

RJ!!!

An interesting way of aliasing TIP#107

I recently gone through something and found a unique way of aliasing. I thought it must be share so other techies also aware of it (or might be you already aware of it).

See below example

SELECT *
FROM (VALUES ('Rajat',30),
             ('Sandeep',40),
             ('Sunil',35),
             ('Shreya',50),
             ('Virendra',45)) AS T(Name,Runs)

Now when you it  you will get following result

I hope you may like this tips.

Enjoy!!!

RJ!!!

A simple way for consistency TIP #106

 

Whenever we develop application of maintain application we define sets of rules or policies  like naming convention , data type, database & SQL SERVER properties (like which property should be unable or disable)  but the problem is to cross check or to enforce these properties is very tedious.

To enforce the policies SQL SERVER provided a great feature which is Policy Based Management.  This is the feature which helps you to not only write the policies or rules but also enforce and cross check whether those rules or policies is followed in your environment or not.

Although these feature is mainly for A DBA but I think it is good for a everyone who love SQL Server.

Now let me share an example which will help us to better understand Policy Based Management.

So to begin with  firstly we have to open the Policy Based Management’s interface. Which we can get in Management folder in SQL SERVER’s object explore window. (You can see below yellow highlighted)

So when you expand the Policy Management in Management feature  You will see 3 different folders which are facets , condition and policies.

So there are  around 84 in build facets which is basically properties for different conditions.

Conditions are basically simple check applied using facets.

Policies are created on condition which will enforce once it created.

Below I am creating policy to check table who has row count =0 (Little bit odd) .You can try with stored procedure name not started with sp_ (will be good start as well).

So , Now create a simple condition by right click and choosing menu New condition

You will get following screen just add condition

We are creating a simple condition which will check the table which has RowCount is 0.

Once you created this condition you will get condition in conditions folder.

Now once condition is created we have to create policy. To create policy we have to right click on policy and select new policy.

When you click the new policy you will get following screen

Now we can add check Condition which we have created as shown in below figure. We can apply policy against target Like in below snap we want policy against every table for IndiandotnetDB

We can set evaluation mode according to our need.

Once you saved the policy we can run it any time.

We can evaluate policy by right click Evaluate as shown in below figure

When we run the policy we will get following result

So , If you see above highlighted row which means a table contain  Row Count.

I hope with above steps you understand a basic way to create Policy Base Management concept.

Policy based management is surely a great tool to manage  database.

Please feel free to give a chance whether you are DBA or not.

Enjoy PBM !!

Happy learning !!

RJ

Merge statement- A simple way for DML TIP#105

When, I first saw this statement a Hindi proverb  come to my mind which is “1 teer 2 nishane” . The meaning of this proverb means a single bow which hit two different aim in one shot.

So let me explain “Merge” statement in more detail. With the help of this Merge statement we can do insert ,update and delete with a single statement.

Let’s understand this by an example. Suppose we have two tables Source and Target as shown in below figure

Now these tables will have some data so lets write query to insert some pre pop data

Now what we want follow things

1) if  employeeId of source and target tables are not matched and if employee name starts with “S” in the source table  then insert the value in target table.  (means insert Sunil & steve’s records from source to destination table)

2) If employeeId of source and target tables are matched then update the Employee name from source table to target table  (if any record matched then update the employee name which not the case with current data)

3) If employeeId of source and target tables are not matched and Employee name in target table starts with “S” then delete that row from target table. (So Sunidhi’s row will be deleted from target table)

Let’s write Merge Statement  for all the 3 above work.

 

Now you observed that there is one more statements which is written explicitly apart from the condition which is OUTPUT clause which helps us to determine what operation is performed.

When you run this you will get following output

Now see the actual data in both the table.

 

So, a simple merge statement is doing all 3 operations like update, insert ,delete.

I hope this tip will help you some where.

Enjoy !!

RJ!!!

Proper Aliasing will help you somewhere TIP#104

Recently, When we were delivering session on “SQL SERVER” one of the persons asked why we require Aliasing so I thought this might be question in everyone’s mind.

So lets start with couple of well know statements then we will see the actual problem where we need it explicitly.

There are two type of aliasing we can do a column aliasing & table aliasing.

Aliasing might help you in readability of stored procedure or function. It helps when you retrieving any calculated or derived column which need in your application so lets starts with some example.

if you see below example we are calculating a column but it does not have column name so fetch this specific value is very difficult so we require column Aliasing here

So as you saw above figure the calculated column is with name “No column name” we can not retrieve it easily so we require aliasing

Now ,lets talk about the table aliasing. So table aliasing help you in readability and it is helpful when you require self join or same table is required in join.

Lets see in below example we did a self join and we required aliasing

The aliasing will be helpful when same table join is required multiple times.

I hope this tip might helpful to someone.

I would appreciate if you provide you inputs as well where we can utilize aliasing.

Enjoy!!!

Th

RJ!!!