based mainly on course notes by Will Hyslop (UNB-F) and course notes by Jeff Ullman and others (Stanford)

Transcription

1 plsql.txt Wed Feb 22 12:40: NOTES ON ORACLE PL/SQL Owen Kaser, February 5, based mainly on course notes by Will Hyslop (UNB-F) and course notes by Jeff Ullman and others (Stanford)

2 plsql.txt Wed Feb 22 12:40: PL/SQL and SQL/PSM: A Sketch Recent SQL standards have augmented SQL to include elements of a conventional programming language (think: like Java, but only one class allowed) Called SQL/PSM. Largely based on Oracle s earlier PL/SQL. Supports variables, loops, if/case, exceptions, methods, arrays, "records". A "cursor" mechanism supports looping through rows. Code invoked explicitly or by a "trigger". See course page for a link to a nice document at Stanford.

3 plsql.txt Wed Feb 22 12:40: Why? ---- Usual application structure (next chapter): SQL statements are sent to database server across network, Carried out on database, Results sent back across network. Can be slow. Would be nice to get more processing done in a single trip to/from server. Package together a whole bunch of stuff to be done, as one operation, on the server.

4 plsql.txt Wed Feb 22 12:40: PL/SQL Block [DECLARE <variable declarations and initializations>] <code involving familiar SQL statments + new stuff> [EXCEPTION <exception handling stuff>] END; e.g. DECLARE fred number := 1; x number; WHILE fred < 10 LOOP UPDATE Mytab_T SET z = 0 WHERE z = fred; dbms_output.put_line( fixing z); fred := fred * 2; END LOOP; END; instead of UPDATE MYtab_T SET z=0 WHERE z IN (1,2,4,8);

5 plsql.txt Wed Feb 22 12:40: Variables Variable types: same as table column types. For strings, use VARCHAR2 or NVARCHAR2. Specify the max length. Declare variables *before* the. Good practice: just accept the type of a table column. Table T, column c s type is "T.c%type" eg myvar T.c%type A query that retrieves a *single row* can set a variable, as follows: SELECT telephone INTO myvar FROM TeaHouse WHERE th_id = 1234; or several: SELECT telephone, th_id INTO myvar, someothervar FROM TeaHouse where th_id = 1234;

6 plsql.txt Wed Feb 22 12:40: Control: Conditionals (examples) IF a=1 THEN CASE b...; WHEN 1 THEN...; ELSIF b>2 THEN WHEN 3 THEN...;...; ELSE...; ELSE END CASE...; END IF; IF a=1 THEN INSERT INTO T VALUES( foo, bar ); a := a + 1; INSERT INTO X VALUES( baz,a); END IF

7 plsql.txt Wed Feb 22 12:40: Control: Loops (examples) LOOP... EXIT WHEN... END LOOP; 2. WHILE condition LOOP... END LOOP; 3. FOR ctr IN [REVERSE] start..end LOOP... END LOOP; eg y := 20; LOOP INSERT INTO X VALUES( something, y); y := y * 2; EXIT WHEN y > 200; END LOOP; -- z does not need to be declared FOR z IN LOOP INSERT INTO X VALUES( blah, z) END LOOP

8 plsql.txt Wed Feb 22 12:40: Cursors: support looping through rows (new concept) A cursor is a mechanism for looping through the rows in a query result, or rows in a table. Read-only access is simplest. Following, an example with cursor named "mycursor". In your local variable definitions use CURSOR mycursor IS <some select statement>; To use the cursor in code, start with OPEN mycursor; To get the next row use FETCH mycursor INTO <list of local vars>; To know if the fetch failed (no more rows) mycursor%notfound is true or false When done using the cursor, use CLOSE mycursor;

9 plsql.txt Wed Feb 22 12:40: Modifying through cursor With table rows, you can modify the table via cursor. DECLARE CURSOR mycurs IS SELECT a,b FROM X where a=3 FOR UPDATE OF b; -- note v1 X.a%TYPE; v2 X.b%TYPE; OPEN mycurs; LOOP FETCH mycurs INTO v1, v2; EXIT WHEN mycurs%notfound; UPDATE X SET b = 52+v1 WHERE CURRENT OF mycur;-- update row at cursor END LOOP CLOSE mycurs; END

10 plsql.txt Wed Feb 22 12:40: Methods aka "Procedures" and "Functions" Procedures are like Java static void methods. Functions are like Java static methods that return values. You declare parameters according to direction of information flow. IN: like Java. Also have OUT and IN OUT. Values assigned to OUT/IN OUT parameters affect caller. CREATE OR REPLACE PROCEDURE myproc( myparam IN OUT int) AS mylocalvar int := 5; INSERT INTO X VALUES( baz, myparam + mylocalval); myparam := mylocalvar; END; (Note: CREATE PROCEDURE replaces DECLARE) When run, a side effect is to make set the caller s parameter variable to 5

11 plsql.txt Wed Feb 22 12:40: Effect of IN OUT and OUT parameters CREATE OR REPLACE PROCEDURE myproc( myparam IN OUT int) AS mylocalvar int := 5; INSERT INTO X VALUES( baz, myparam + mylocalval); myparam := mylocalvar; END;... more stuff later... DECLARE x int := 20; myproc(x); -- invoke it dbms_output.put_line( x value is x not 20 ); END If you run that block, you get x value is 5 not 20

12 plsql.txt Wed Feb 22 12:40: Nested Procedures You can declare a procedure within a procedure. Put it in the same place as the variable declarations for a procedure, AFTER all of the variable declarations CREATE PROCEDURE outer (x IN int) AS v1 int := 2; PROCEDURE innner( y IN OUT int) AS y := y + 1; END; innner(v1); dbms_output.put_line( v1 is now v1); END;

13 plsql.txt Wed Feb 22 12:40: Function Function is like procedure, except that it will return a value. CREATE FUNCTION foo( str IN varchar2, y IN int) RETURN int AS UPDATE X SET col1 = str WHERE col2=y; RETURN SQL%ROWCOUNT; END notes: 1. parameter str cannot indicate length of varchar2 2. SQL%ROWCOUNT is number of rows updated

14 plsql.txt Wed Feb 22 12:40: Exceptions PL/SQL has exceptions. Eg, one is raised if you try to do a SELECT... INTO and the query returns no row. EXCEPTION -- handling some exceptions WHEN NO_DATA_FOUND THEN dbms_output.put_line( oops, select into failed! );... WHEN ZERO_DIVIDE THEN... WHEN OTHERS THEN... You can RAISE your own exceptions (details omitted). You can abort your PL/SQL code with RAISE_APPLICATION_ERROR(<num>,<string err msg>); use numbers between and

15 plsql.txt Wed Feb 22 12:40: Making Code Run use interactive command EXEC <procedure name>(param1, param2,...); just says "anonymous block completed :( 2. set up a trigger, and do something that fires it CREATE TRIGGER mytrig BEFORE UPDATE OR DELETE ON TeaHouse FOR EACH ROW WHEN (NEW.TH_ID > 5) -- a PL/SQL block IF :NEW.phone!= :OLD.phone THEN -- new and :new are builtin, mean the new version -- of a changed row. :old and old are similar. dbms_output.put_line( phone number change! ; END IF; END; UPDATE TEAHOUSE SET phone= WHERE th_id=6;

16 plsql.txt Wed Feb 22 12:40: Creating procedures in SQL Developer In left pane, right click on Procedures, choose New Procedure. It will guide you through the parameter creation and make a skeleton that you fill in. Do File/Save (or ^S) to compile. Error msgs in bottom pane. To run, use green triangle. Fill in your parameters after the =>, for IN parameters. Not sure about OUTs. Your output is in the bottom pane. Function creation is similar.

17 plsql.txt Wed Feb 22 12:40: