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Cursor

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Cursor

  1. 1. Cursors in SQL proceduresIn SQL procedures, a cursor make it possible to define a result set (aset of data rows) and perform complex logic on a row by row basis. Byusing the same mechanics, an SQL procedure can also define a result setand return it directly to the caller of the SQL procedure or to a clientapplication.A cursor can be viewed as a pointer to one row in a set of rows. Thecursor can only reference one row at a time, but can move to other rowsof the result set as needed.To use cursors in SQL procedures, you need to do the following:1.Declare a cursor that defines a result set.2.Open the cursor to establish the result set.3.Fetch the data into local variables as needed from the cursor, one rowat a time.4.Close the cursor when doneTo work with cursors you must use the following SQL statements:•DECLARE CURSOR•OPEN•FETCH•CLOSEThe following example demonstrates the basic use of a read-only cursorwithin an SQL procedure: CREATE PROCEDURE sum_salaries(OUT sum INTEGER) LANGUAGE SQL BEGIN DECLARE SQLSTATE CHAR(5) DEFAULT 00000; DECLARE p_sum INTEGER; DECLARE p_sal INTEGER; DECLARE c CURSOR FOR SELECT SALARY FROM EMPLOYEE; SET p_sum = 0; OPEN c; FETCH FROM c INTO p_sal; WHILE(SQLSTATE = 00000) DO SET p_sum = p_sum + p_sal; FETCH FROM c INTO p_sal; END WHILE; CLOSE c; SET sum = p_sum;
  2. 2. END;;

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