教学讲稿oracle官方ref.pptxVIP

REF Cursors Cursor Variables Cursor variables are like C or Pascal pointers, which hold the memory location (address) of an item instead of the item itself. In PL/SQL, a pointer is declared as REF X, where REF is short for REFERENCE and X stands for a class of objects. A cursor variable has the data type REF CURSOR. A cursor is static, but a cursor variable is dynamic. Cursor variables give you more flexibility. Using Cursor Variables You can use cursor variables to pass query result sets between PL/SQL stored subprograms and various clients. PL/SQL can share a pointer to the query work area in which the result set is stored. You can pass the value of a cursor variable freely from one scope to another. You can reduce network traffic by having a PL/SQL block open (or close) several host cursor variables in a single round-trip. Defining REF CURSOR Types Define a REF CURSOR type: Declare a cursor variable of that type: Example: Define a REF CURSOR type TYPE ref_type_name IS REF CURSOR [RETURN return_type]; ref_cv ref_type_name; DECLARE TYPE DeptCurTyp IS REF CURSOR RETURN departments%ROWTYPE; dept_cv DeptCurTyp; Using the OPEN-FOR, FETCH, and CLOSE Statements The OPEN-FOR statement associates a cursor variable with a multirow query, executes the query, identifies the result set, and positions the cursor to point to the first row of the result set. The FETCH statement returns a row from the result set of a multirow query, assigns the values of select-list items to corresponding variables or fields in the INTO clause, increments the count kept by %ROWCOUNT, and advances the cursor to the next row. The CLOSE statement disables a cursor variable. Example of Fetching DECLARE TYPE EmpCurTyp IS REF CURSOR; emp_cv EmpCurTyp; emp_rec employees%ROWTYPE; sql_stmt VARCHAR2(200); my_job VARCHAR2(10) := ST_CLERK; BEGIN sql_stmt := SELECT * FROM employees WHERE job_id = :j; OPEN emp_cv FOR sql_stmt USING my_job;