Cursor in sql

DECLARE CURSOR defines the attributes of a Transact-SQL server cursor , such as its scrolling behavior and the query used to build the result set on which the cursor operates. The OPEN statement populates the result set, and FETCH returns a row from the result set. A cursor holds the rows (one or more) returned by a SQL statement. The set of rows the cursor holds is referred to as the active set. A SQL cursor is a database object that retrieves data from result sets one row at a time.

The cursor in SQL can be used when the data needs to be updated row by row. A cursor is a temporary work area created in system memory when an SQL statement is executed. It is a database object to retrieve data from a result set one row at a time.

This is where cursors come into play. A database cursor is an object that enables traversal over the rows of a result set. It allows you to process individual row returned by a query.

SQL Server cursor life cycle. Opening a cursor on a result set allows processing the result set one row at a time. You can assign a cursor to a variable or parameter with a cursor data type. A cursor contains information on a select statement and the rows of data accessed by it.

This temporary work area is used to store the data retrieved from the database, and manipulate this data. A Cursor is a pointer to this context area. Oracle creates context area for processing an SQL statement which contains all information about the statement.

Normally, the cursor is used when we need to process multiple rows of data. Cursor in SQL To execute SQL statements, a work area is used by the Oracle engine for its internal processing and storing the information. This work area is private to SQL’s operations.

The pointer can be moved from one row to the next. Depending on the type of cursor , you may be even able to move it to the previous row. With it, you can reach into the bag and grab a row, and then move onto the next.

It is a temporary area for work in memory system while the execution of a statement is done. It instead uses comparisons of timestamp column values, or a checksum value if the table has no timestamp column, to determine whether the row was modified after it was read into the cursor. The name of this context area is same as the cursor name. T- SQL : A Simple Example Using a Cursor.

SQL cursors and query expressions You can use any legal SELECT statement as a query expression. The rows that the SELECT statement retrieves are the ones that the cursor steps through one at a time. Cursor can also be defined as a set of rows together with a pointer that identifies a current row. These rows are the scope of the cursor. SQL cursors are primarily used where set-based operations are not applicable and you are required to access data and perform operations one row at a time rather than applying a single set-based operation to an entire object (such as a table or a set of tables).

Cursors are very bad for performance, and should be avoided always. Most of the time, cursors can be very easily replaced using joins. There are different types of cursors in sql server as listed. While a cursor is being populate the table being iterated is locked. Row operations can take a long time to execute depending upon the type of task being performed on each row.

While the cursor is open, a table cannot be accessed or updated by the other users. This makes cursor -based operations extremely.