What are the difference between DDL, DML and DCL commands?

DDL – Data Definition Language: statements used to define the database structure or schema. Some examples:

• CREATE – to create objects in the database
• ALTER – alters the structure of the database
• DROP – delete objects from the database
• TRUNCATE – remove all records from a table, including all spaces allocated for the records are removed
• COMMENT – add comments to the data dictionary
• RENAME – rename an object

They are called Data Definition since they are used for defining the data. That is the structure of the data is known through these DDL commands.

DML – Data Manipulation Language: statements used for managing data within schema objects. Some examples:

• SELECT – retrieve data from the a database
• INSERT – insert data into a table
• UPDATE – updates existing data within a table
• DELETE – deletes all records from a table, the space for the records remain
• MERGE – UPSERT operation (insert or update)
• CALL – call a PL/SQL or Java subprogram
• EXPLAIN PLAN – explain access path to data
• LOCK TABLE – control concurrency

DML commands are used for data manipulation. Some of the DML commands
insert,select,update,delete etc. Even though select is not exactly a DML language command oracle still recommends you to consider SELECT as an DML command.

DML are not auto-commit. i.e. you can roll-back the operations, but DDL are auto-commit

DCL – Data Control Language. Some examples:

• GRANT – gives user’s access privileges to database
• REVOKE – withdraw access privileges given with the GRANT command

Data Control Language is used for the control of data. That is a user can access any data based on the priveleges given to him. This is done through DATA CONTROL

It is used to create roles, permissions, and referential integrity as well it is used to control access to database by securing it.

TCL – Transaction Control: statements used to manage the changes made by DML statements. It allows statements to be grouped together into logical transactions.

• COMMIT – save work done
• SAVEPOINT – identify a point in a transaction to which you can later roll back
• ROLLBACK – restore database to original since the last COMMIT
• SET TRANSACTION – Change transaction options like isolation level and what rollback segment to use

For revoking the transactions and to make the data commit to the database we use TCL.

Once we commit we cannot rollback. Once we rollback we cannot commit.

Commit and Rollback are generally used to commit or revoke the transactions that are with regard to DML commands.

Source: From different sql experts from internet

You can get variable from javascript and use it in code behind code in dotnet variable it means server side variable.

Dim strMessage2 As String = “”

Response.Write(“var str1 =
prompt(‘Please Enter Password:’,”);”)

strMessage2 = “document.write(str1);”

Response.Write(strMessage2)

http://stackoverflow.com/questions/tagged/index

Some really usefull Short keys in SQL
Next Page F6
previous Pane Shift F6
Hide/Show Result Pane CTRL R

Searches expression2 for expression1 and returns its starting position if found. The search starts at start_location.

Few good scripts with charindex

select CHARINDEX(‘a’, ‘india’)

–result will be 5

select CHARINDEX( ‘,1,’ ,’,1,2,3,’)
– result would be 3
DECLARE @selectedID VARCHAR(10)
SET @selectedID = ‘1,2′
–SET @selectedID = ‘1,5′

Some times we have to pass comma seprated value to sp and have to cross check with table data, its good script here.

it would give you all records which are passed in parameter @selectedID.

DECLARE @t AS TABLE (tID INT)
INSERT INTO @t VALUES (1)
INSERT INTO @t VALUES (2)
INSERT INTO @t VALUES (3)

SELECT * FROM @t
WHERE  CHARINDEX(‘,’ + CONVERT(VARCHAR(5),tID) + ‘,’, ‘,’ + @selectedID + ‘,’) > 0

I read one good article about sql server – transaction isolation level..

You might like it

Articl Summary: This post discusses the basics of SQL Server Transaction Isolation Levels.

http://www.sqlserverandxml.com/2008/08/introduction-to-sql-server-transaction.html

i have read one good blog which explains basics of query process. Here is the order in which query operators are evaluated. There are 11 levels.

1. FROM
2. ON
3. JOIN
4. WHERE
5. GROUP BY
6. WITH{CUBE | ROLLUP}
7. HAVING
8. SELECT
9. DISTINCT
10. HAVING
11. TOP

First the query processor reads all the rows from the FROM the left table and apply the ON condition with the right table provided in JOIN.

If there are more JOINs the same is done for all the JOINs.

Then the WHERE clause is applied to filter rows.

Then GROUP BY is done

There WITH clause get evaluated followed by HAVING.

Then the columns are selected. (This is the reason why you cannot use a column alias in WHERE or GROUP BY)

Then DISTINCT clause applied

Then ORDER BY is processed…(This is the reason why you CAN use a column alias in the ORDER BY clause)

Then TOP clause get evaluated.

SOURCE : http://knowledgebaseworld.blogspot.com/2008/07/query-operators-evaluation.html

SOURCE : http://www.dotnetspider.com/resources/1521-How-call-Postback-from-Javascript.aspx

Introduction

Postback is a concept introduced in ASP.NET and is a very handy method. Postback is built into the ASP.NET and most of the web controls support it without writing any code.

Calling postback event from Javascript

There may be some scenario where you may want to explicitly postback to the server using some clientside javascript. It is pretty simple to do this.

ASP.NET already creates a client side javascript method as shown below to support Postbacks for the web controls:

function __doPostBack(eventTarget, eventArgument) {
if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
theForm.__EVENTTARGET.value = eventTarget;
theForm.__EVENTARGUMENT.value = eventArgument;
theForm.submit();
}
}

So, all you have to do is, just call this method with appropriate arguments. You may call this as shown below:

<script language=’Javascript’>
__doPostBack(‘__Page’, ‘MyCustomArgument’);
</script>

However, it is not reccommdended to use this method name directly in the client side. The best approach is, generate this piece of code from the code behind file using ASP.NET. This way, you are safe even if Microsft later change the name of the method ‘__doPostBack’ to something else in a future release.

In your code behind file, declare a protected variable as shown below:

Protected PostBackStr As String

Now, in the page load event, write the following code:

PostBackStr = Page.ClientScript.GetPostBackEventReference(Me, “MyCustomArgument”)

The method GetPostBackEventReference() will generate the same piece of client side code that you need to use to call the Postback method. Instead of harcoding the method name __doPostBack, we are asking ASP.NET to tell us what is the method name.

Now insert the following code in your Aspx page:

<script language=’Javascript’>
<%= PostBackStr %>
</script>

At runtime, it will be evaluated as:

<script language=’Javascript’>
__doPostBack(‘__Page’, ‘MyCustomArgument’);
</script>

Remember to insert the above script into some Javascript method/event where you want to call the postback, instead of simply inserting into the page as shown above.

Generaly, when we do any search in application , we make edit from there of specific record in new popup. We do save in popup and close that popup and refresh our parent search page, then if we wanted to make search by default, we can use this method by refreshing page with search button control.

How to identify and handle the postback in code behind ?

You found how to call the postback from javascript. Now you need a way to identify your postback in the code behind file. The second argument the doPostback method becomes helpful here.

Go to the code behind file and write the following code in the Page Load event:

If Page.IsPostBack Then
Dim eventArg As String = Request(“__EVENTARGUMENT”)
If eventArg = “MyCustomArgument” Then
Response.Write(“You got it !”)
End If
End If

Did you notice how we identify if the page is loaded as part of our postback? We used the second argument in the __doPostBack method to pass a value and used that in PageLoad to identify if it is called as a result of our PostBack.