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To add to Jorgen's answer, I've always wondered why SQL Server doesn't allow us to use alias in WHERE and HAVING clauses. The answer to that lies in the logical order in which the query is processed. The WHERE and HAVING clauses are processed before the SELECT clause and the alias do not exist at that stage.
However, technically it should be possible to introduce another stage earlier in the query processing pipeline where a mapping between expressions and their alias is made and WHERE and HAVING clauses can look up to these mappings and substitute the actual expression in place of the alias.
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You are looking for CTE.
"The ones who care enough to do it right care too much to compromise."
Matthew Faithfull
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Yes, or a simple
SELECT ... FROM
(
SELECT ... FROM table WHERE ...
) T
...
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Yes, thats equivalent. I just prefer the readability of the CTE (which is merely an opinion) plus that you can refer to a CTE in more than one place.
"The ones who care enough to do it right care too much to compromise."
Matthew Faithfull
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Ado.net is the Library in .net technology. this library help to you for connect your application to the database.
- Now Come in depth
C# is a language. and responsible to create the User Interface like Console, Web, and Window Application.
SQL is also language for create the database and database store the data.
Suppose i need to connect my Front-End to the Back-End.
or We say that C# Communicate to the SQL. now its not possible to two different language communicate to each other. Simple Example is
One Person is Russian and second is Indian now they want to talk to each other. Big Problem Occur when they want to communicate because Russian not known the Hindi language and similar Indian not know the Russian Language. now both person need to mediator or Converter. Converter convert the language means for Indian to Hindi and Russian to Russian Language.
-----Ado.Net Mediator between the Front-End to the Back-End-----
Ado.Net is provider to make the connection between the Front-End to the Back-End.
Thank you
Student of Dr. Sandeep Karan CAC Noida
Himanshu Sharma
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And what is your question?
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That's not a question, it's a Tip (or atleast he thinks so)
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This is really a great tip for the beginners.
i thank you from all the Beginners those who need a Elaborated definition to understand the concepts..
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What is the difference between truncating and deleting a table?
After the truncating or deleting do we need to re-index or shrink the table?
We are looking to do some clean-up on some rather large tables on our database. Once we do the clean-up what steps do we need to preform for overall database "health"?
Thanks!
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mrfalk wrote: re-index
If there's no records left, there's little to reindex.
mrfalk wrote: What is the difference between truncating and deleting a table?
Google "MSDN Truncate", and from the manual we learn;
Removes all rows from a table without logging the individual row deletions. TRUNCATE TABLE is similar to the DELETE statement with no WHERE clause; however, TRUNCATE TABLE is faster and uses fewer system and transaction log resources.
Bastard Programmer from Hell 
If you can't read my code, try converting it here[^]
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So if we are using the Delete statement with the WHERE clause is it necessary to reindex? Is there a "standard" for when to reindex files?
After further research we will be using the delete clause because we want to retain a given number of days data. Within that given number of days data we will also be deleting specific rows based on a given parameter. We just want to make sure we are covering all bases.
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mrfalk wrote: So if we are using the Delete statement with the WHERE clause is it necessary to reindex?
Yes.
mrfalk wrote: Is there a "standard" for when to reindex files?
No.
Start here[^].
Bastard Programmer from Hell
If you can't read my code, try converting it here[^]
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Truncate statement:
1. Deletion is very faster. Almost no (very minimal) transaction log is produced during this operation.
2. Data pages which are used by the table are de allocated for further use by SQL Server in other operations.
3. Identity column value is reset from its original default position. For example if a table has an identity column and identity value start form 1 then after running truncate command the value start incrementing back from 1.
4. As wiping out rows are very faster, so the number of locks are low. Although during TRUNCATE operation table and page lock happens but not each row.
5. TRUNCATE TABLE command does not support where clause, it also does not works if foreign key exists in the table. In addition, table participates in log shipping or replication also does not honor TRUNCATE table command.
6. Records removed by the TRUNCATE COMMAND cannot be restored even though the database recovery model is set to FULL.
7. TRUNCATE statement also does not fire triggers.
DELETE Statement:
1. The DELETE statement removes rows one at a time. For each deleted row the operation writes an entry in the transaction log.
2. DELETE operation is more resource intensive thus consumes more database resources and locks.
3. Where clause can be included with the statement to restrict the number of affected rows.
4. Internally the DELETE operation does not cleanup rows immediately if the table has any index on it, The operation marks the affected rows "to be deleted". The marked records are known as GHOST RECORDS. Although these records are de allocated quickly by a background cleanup process for better performance.
dsdf
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Truncating will also reset the seed for any identity column, whereas delete will not.
-NP
Never underestimate the creativity of the end-user.
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We have found that for integrated security through VB.NET the DELETE works with less permissions. The error you get back when using TRUNCATE gives no indication as to truncate being the problem.
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Hi,
-- DELETE, TRUNCATE and DROP Statements
DELETE
/*
The DELETE command is used to remove rows from a table.
A WHERE clause can be used to only remove some rows.
If no WHERE condition is specified, all rows will be removed.
After performing a DELETE operation you need to COMMIT or ROLLBACK the transaction to make the change permanent or to undo it.
Note that this operation will cause all DELETE triggers on the table to fire.
*/
TRUNCATE
/*
TRUNCATE removes all rows from a table.
The operation cannot be rolled back and no triggers will be fired.
As such, TRUCATE is faster and doesn't use as much undo space as a DELETE.
*/
DROP
/*
The DROP command removes a table from the database.
All the tables' rows, indexes and privileges will also be removed.
No DML triggers will be fired. The operation cannot be rolled back.
*/
--Difference between TRUNCATE and DELETE commands
/*
1) TRUNCATE is a DDL command whereas DELETE is a DML command.
2) TRUNCATE is much faster than DELETE.
Reason:When you type DELETE.all the data get copied into the Rollback Tablespace first.then delete operation get performed.Thatswhy when you type ROLLBACK after deleting a table ,you can get back the data(The system get it for you from the Rollback Tablespace).All this process take time.But when you type TRUNCATE,it removes data directly without copying it into the Rollback Tablespace.
Thatswhy TRUNCATE is faster.Once you Truncate you cann't get back the data.
3) You cann't rollback in TRUNCATE but in DELETE you can rollback.
TRUNCATE removes the record permanently.
4) In case of TRUNCATE ,Trigger doesn't get fired.
But in DML commands like DELETE .Trigger get fired.
5) You cann't use conditions(WHERE clause) in TRUNCATE.
But in DELETE you can write conditions using WHERE clause
*/
Regards,
GVPrabu
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Hi Guys,
I want to know the table creation for the problem described below.
I have a 26 parameters for a customer feed back,
and i have a set of sites , some sites don't have some parameters in my 26 points, and some site want more then 26 points,
so i thought to create table like
id(int),parametename(Nvarchar(max)),site1(bit),site2(bit),site3(bit),site4(bit)
and i will allow in UI to check which point is applicable for which site,
this solution is for time being,
my concern is id the site name may add in future that time we have to change the parameter table and modify the insert and update methods as well as Store procedure,
How can avoid the re-coding by creating customized table.
Please suggest me the solution.
Thanks and regards
Vishwa
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You should have a table that stores the list of sites identified by a SiteID column. And then you can store the values in your table with these columns
id(int),parametename(Nvarchar(max)),SiteID(int),value(bit)
Whenever there is a new site is to be added, just add it to the site table and insert a new row with that id in this table.
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Table: site
- id
- Site_name
- Site_url
Table: site_parameter
- id
- Site_id (foreign key to above table)
- name
- value
For "26 parameters" you would have 26 rows in the site_parameter table.
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Hi
I have an employee table with column gender F and M. Now i want to update the gender values of all the employee as F with M and M with F. But this should happen in a single query. How can i do this.
Thanks for your help.
Regards
Naina
Naina
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You cannot do it in a single query, you need 3 updates, move F to X, move M to F, move X to M you can wrap the 3 queries in a transaction to insure integrity is maintained.
Never underestimate the power of human stupidity
RAH
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Mycroft Holmes wrote: You cannot do it
You can actually do it. SQL is a set based language, changes made in a query are either fully committed or fully rolled back, there is no partial update. So, Eddy's solution will actually work.
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Eddie got my 5, I didn't think of using case statement in the update clause.
Never underestimate the power of human stupidity
RAH
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BEGIN TRANSACTION
CREATE TABLE Person
(
Name VARCHAR(MAX)
,Gender CHAR(1)
)
INSERT INTO Person VALUES
('Pete', 'M')
,('John', 'M')
,('Mary', 'F')
,('Dude', 'M')
,('Mary', 'F')
SELECT *
FROM Person
UPDATE Person
SET Gender = CASE Gender WHEN 'M' THEN 'F'
ELSE 'M'
END
SELECT *
FROM Person
ROLLBACK
Bastard Programmer from Hell
If you can't read my code, try converting it here[^]
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