When do you need to use cursors in SQL? To use cursors

cursors are generally used to use the contents of the result set obtained through scripts in other SQL statements. However, cursor execution will affect the execution speed of scripts, so please be careful when using it. The typical process of using SQL cursors in stored procedures or triggers is to declare that SQL variables contain data returned by cursors. Declare a variable for each result set column. Declare a variable large enough to hold the value returned by the column, and declare the type of the variable as a data type that can be implicitly converted from the column data type.

use the DECLARE CURSOR statement to associate the SQL cursor with the SELECT statement. In addition, the DECLARE CURSOR statement also defines the characteristics of the cursor, such as the cursor name and whether the cursor is read-only or forward-only.

use the OPEN statement to execute the SELECT statement and populate the cursor.

use the FETCH INTO statement to extract a single row and move the data in each column to the specified variable. Then, other SQL statements can reference those variables to access the extracted data values. SQL cursors do not support fetching row blocks.

use the CLOSE statement to end the use of the cursor. Closing the cursor can release some resources, such as the cursor result set and its lock on the current row, but if an OPEN statement is reissued, the cursor structure can still be used for processing. Because the cursor still exists, the name of the cursor cannot be reused at this time. The DEALLOCATE statement completely releases the resources allocated to the cursor, including the cursor name. After releasing the cursor, you must use the DECLARE statement to regenerate the cursor.