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What is Cursor in SQL, and How to Implement it? 

A temporary memory or temporary workstation in SQL is known as a cursor. When you perform a data manipulation language (DML) action on the table, the database server will allocate the cursor. 

Cursors manipulate data in any database set, which you can do one row at a time. To manage the dataset, you must write a SQL SELECT statement for the cursor to fetch a row set from the database set.

What are the Different Types of Cursors? 

There are two types of cursors, and they are as below:

●     Implicit Cursors

The default cursors of the SQL servers are known as Implicit cursors. When the user begins to perform DML operations, the SQL server allocates the implicit cursors.

For example, you can allot these cursors during queries such as INSERT, DELETE, and UPDATE. In addition, the SQL server generates the implicit cursor when the SELECT command selects any row. 

● Explicit Cursors

Explicit cursors, on the other hand, are user generated. You can use these cursors for fetching data from any table in a row-to-row format.

Users who work on SQL and require a cursor can generate an explicit cursor. The user will have to give a SELECT command for generating explicit cursors. 

How to Implement or Use a Cursor?

A user can only create an explicit cursor since the implicit cursor is system generated. Therefore, a user will have to follow the below steps to implement an explicit cursor:

●     Declaring a Cursor Object

In this step, the user must declare the variables and return a set of values. For example, you can do as follows:

DECLARE cursor_name CURSOR FOR SELECT* FROM (table_name – mention the name of your table from where you fetch the data)

●     Open Cursor Connection

It is called the entering stage of the cursor, and the command used is OPEN cursor_connection. 

● Fetching data from the cursor

This phase retrieves data with a cursor, which you can do in a row-to-row format. You can do fetching in six different methods:

●  FIRST- it is used to fetch only the first row.

●  LAST – It is used to fetch only the last row.

●  NEXT – It is used to fetch data in the forward direction.

●  PRIOR – It is used to fetch data in backward order.

●  ABSOLUTE n – It fetches data from the same nth row.

●  RELATIVE n – It fetches data in incremental and decremental ways.

The command used in this step would be FETCH (any of the six options such as FIRST, RELATIVE, etc.) (cursor name). 

● Closing

It is the phase when the cursor is closed, and the syntax used is CLOSE (cursor name). 

● Deallocate

It is the last step in which you delete all the cursor definitions and release all the system resources linked to the cursor. The command used is DEALLOCATE (cursor name). 

Wrapping up

A cursor is used in any SQL to help manipulate data in different datasets. Handling data row by row through the cursor becomes easy, especially when working with large datasets. With the help of cursors, you can easily update, insert, or even delete records on your specified conditions. You can even use cursors when doing complex calculations on your data. To learn more, visit education nest.

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