Execute Dynamic SQL commands in SQL Server

-
In some applications having hard-coded SQL statements is not appealing, because of the dynamic nature of the queries being issued against the database server. Because of this sometimes there is a need to dynamically create a SQL statement on the fly and then run that command. This can be done quite simply from the application perspective where the statement is built on the fly whether you are using ASP.NET , ColdFusion or any other programming language. But how do you do this from within a SQL Server stored procedure? SQL Server offers a few ways of running a dynamically built SQL statement. These ways are: Writing a query with parameters Using EXEC Using sp_executesql Writing a query with parameters This first approach is pretty straightforward if you only need to pass parameters into the WHERE clause of your SQL statement. Let’s say we need to find all records from the Customers table where City = ‘London’. This can be done easily as the following example shows. ...
Post a Comment

Delete Duplicate rows from the table.

-
Delete Duplicate rows from the table.
Suppose there is a table called "EmployeeTable" which have some duplicate records.
There is a three way to delete the duplicate rows.

First way to delete duplicate rows :


Select distinct * into Emp_Temp_Table from EmployeeTable

In the above line we are inserting all the distinct row of the "EmployeeTable" to another table "Emp_Temp_Table" (Emp_Temp_Table will create automatically when you use the above query.)
Actuall the above query create clone of EmployeeTable and insert all the distinct row inside the Clone Table (Emp_Temp_Table).


drop table EmployeeTable

sp_rename 'Emp_Temp_Table',EmployeeTable'

Then Delete the orginal table and rename the clone table with the name of orginal table.


Second way to delete duplicate rows :

Select distinct * into Emp_Temp_Table from EmployeeTable

Truncate table EmployeeTable

insert into EmployeeTable select * from Emp_Temp_Table

drop table Emp_Temp_Table


Third way to delete duplicate rows :

Populate the new Primary Key


Alter table EmployeeTable add NewPK int NULL
Go
Declare @intCounter int
Set @intCounter = 0
Update EmployeeTable
SET @intCounter = NewPK = @intCounter + 1

Select name,RecCount=count(*), PktoKeep = max(NewPK)
Into #dupes
From EmployeeTable
Group by name
Having count(*) > 1
Order by count(*) desc

Delete dupes except one Primary key for each dup record


Delete test
from EmployeeTable a join #dupes d
a.name
where a.NewPK not in (select PKtoKeep from #dupes)


Remove the NewPK column


ALTER TABLE test DROP COLUMN NewPK
go

drop table #dupes

Comments

Sapien said…
This is the best, no nonsense, and most simplistic answer I've seen so far. That one line created the table, with all the right columns for me, then I just renamed the old table and it's done. Thanks.
October 2, 2008 at 6:15 AM
rana said…
tahnks.
This is very good query.I have asked this question my time in interview.It very simple to remember.
February 17, 2011 at 11:15 PM
Post a Comment

Popular posts from this blog

Check If Temporary Table Exists

-
When working with temporary tables in SQL Server, the common conundrum is often determining whether a temp table exists before performing operations on it. In this blog post, we’ll delve into the nuances of checking the existence of temp tables and explore the potential pitfalls and solutions. The Basics: Local Temp Tables To check if a local temp table exists, one commonly used approach is: IF OBJECT_ID ( 'tempdb..#temp' ) IS NOT NULL BEGIN PRINT '#temp exists!' END ELSE BEGIN PRINT '#temp does not exist!' END This method utilizes the OBJECT_ID function to verify the existence of the temp table in the tempdb database. The Undocumented Second Parameter An alternative way involves an undocumented optional second parameter: IF OBJECT_ID ( 'tempdb..#temp' , 'u' ) IS NOT NULL BEGIN PRINT '#temp exists!' END ELSE BEGIN PRINT '#temp does not exist!' END However, it’s important to no...
Read more

Multiple NULL values in a Unique index in SQL

-
this project needed to support having multiple NULL values in the column and still have a UNIQUE constraint . That is allowed by Oracle but not in SQL Server and DB2 LUW. There is a way to make this work in SQL Server and DB2 LUW also but that requires a work -around. Consider this table : CREATE TABLE TEST_UQ (COL1 INT IDENTITY (1,1) PRIMARY KEY , COL2 NVARCHAR(10) NULL ) GO In this table , COL1 has been declared as the primary key but we want a UNIQUE constraint to be put on COL2 as well. Please note that COL2 is a nullable column and that SQL Server does not allow multiple NULL values in a UNIQUE index and treats them the same way. We can test it out prior to proceeding with the work -around: Let tus create a unique index first : CREATE UNIQUE INDEX TEST_UQ_IND_1 ON TEST_UQ (COL2) GO Now, let us try to insert these values : insert into test_uq (col2) values (’abc’); insert into test_uq (col2) values (’xyz’); insert into ...
Read more

How To search entire database?

-
While browsing the SQL Server newsgroups, there are occasional requests for a script capable of searching all the columns of all the tables in a given database for a specific keyword. Although it might seem trivial, the need for such a script became apparent in a real-world scenario. In troubleshooting a problem with Microsoft Operations Manager (MOM), which utilizes SQL Server for storing computer, alert, and performance-related information, a network administrator needed to search all the MOM tables for a specific string. Lacking a readily available script, manual searching ensued. This experience prompted the creation of a stored procedure called “SearchAllTables.” SearchAllTables Stored Procedure The SearchAllTables stored procedure takes a search string as an input parameter and systematically searches all char , varchar , nchar , and nvarchar columns of all tables (excluding system tables) owned by all users in the current database. Feel free to extend this procedure to sea...
Read more