h.melikian1 plsql dr.hayk melikyan departmen of mathematics and cs [email protected]
TRANSCRIPT
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Program StructurePL/SQL like other programming languages,
groups itsstatements into units called BLOCKS. Blocks can
beunnamed (anonymous ) or named ( sub-
programs).The subprograms can be either functions or proceduresand they can be grouped into a packages.
PL/SQL also allows access to databases via the cursors,
triggers, stored procedures and functions.
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Basic Structure of
DECLARE -- Declarative section: -- variables, types, and local subprograms. BEGIN -- Executable section: -- procedural and SQL statements go here /* the only section of the block that is required. */
EXCEPTION -- Exception handling section: -- error handling statements go here END
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What You Can and can’t ?
The only SQL statements allowed in a PL/SQL program are
SELECT, INSERT, UPDATE, DELETE and several other
The SELECT statement has a special format.
CREATE, DROP, or ALTER are not allowed.
PL/SQL is not case sensitive
C style comments (/* ... */) or ( -- ….) .
To execute a PL/SQL program, we must follow the program text
itself by a line with a single dot ("."),
and then a line with run;
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PL /SQL: Datatypes and Variables
DESCRIPTION ( scalar data types)Numeric BINARY INTEGER Integer in the range -231 - 1 to
231 -1. NATURAL Integer in the range 0 to
231
POSITIVE Integer in the range 1 to 231
NUMBER(p,s) Same as Oracle SQL's NUMBER,
where p is the precision and s is the scale
Character CHAR(N) Fixed-length character string of length N. VARCHAR2(N) Variable-length character string of
maximum length N Boolean BOOLEAN Boolean data typ (TRUE, FALSE) Date-Time DATE Same as Oracle SQL's DATE
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Variables and TypesThat type can be
One of the types used by SQL for database columns
A generic type used in PL/SQL such as NUMBER
Declared to be the same as the type of some database column
DECLARE
price NUMBER;
myBeer VARCHAR(20);
or
DECLARE
myBeer Beers.name%TYPE;
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Variables and Types(2)
A variable may also have a type that is a record with several
fields. The simplest way to declare such a variable is to use
%ROWTYPE on a relation name DECLARE beerTuple Beers%ROWTYPE; The initial value of any variable, regardless of its
type, is NULL.
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PL/SQL: Anchored Declarations
cnum customers.cno%type; cname customers.cname%type; commission REAL(5,2) := 12.5; x commission%type;Anchored variables are synchronized with the
database columns. The database columns may change their datatypes and the PL/SQL program remains compatible.
Anchored variables declared within the PL/SQL program are normalized, i.e. changing one data type does not a_ect how the corresponding anchored variables will be used.
Anchored data types are evaluated at compile time.
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Variables and Types(3)
We can assign values to variables, using the ":=" operator. The
assignment can occur either immediately after the type of the
variable is declared, or anywhere in the executable portion of the
program. An exampl
DECLARE
a NUMBER := 3;
BEGIN
a := a + 1;
END;
.
run;
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PL/SQL: Variable/Constant Declarations
i BINARY_INTEGER; cno NUMBER(5) NOT NULL := 1111; cname VARCHAR2(30); commision NUMBER(5,2) := 12.5; MAXCOLUMNS CONSTANT INTEGER(2) := 30; hired_date DATE; done BOOLEAN;Any variable that is declared to be NOT NULL
must be initialized in its declaration.All variables that are not defined to be NOT
NULL are initialized to have the value NULL.
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Simple Programs in PL/SQL
After the SELECT clause, we must have an INTO clause listing
variables, one for each attribute in the SELECT clause, into
which the components of the retrieved tuple must be placed.
CREATE TABLE T1( e INTEGER, f INTEGER );
DELETE FROM T1;
INSERT INTO T1 VALUES(1, 3);
INSERT INTO T1 VALUES(2, 4);
Above is plain SQL; below
.
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NEXTDECLARE
a NUMBER;
b NUMBER;
BEGIN
SELECT e,f INTO a,b FROM T1 WHERE e>1;
INSERT INTO T1 VALUES(b,a);
END;
.
run;
/*this is the PL/SQL program
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Control Flow in PL/SQLThere are three
version of of statement in
PL/SL:if-then: IF <condition> THEN
<statement_list>
END IF;
if-then-else:
IF <condition> THEN <statement_list>
ELSE
<statement_list>
END IF;
if (cnum > 10) and (cnum < 90) then i := i + 1; dbms_output.put_line('Cust ' || cnum);end if;
if (cnum > 10) and (cnum < 90) then i := i + 1; dbms_output.put_line('Valid Cust ' || cnum); else j := j + 1; dbms_output.put_line('Invalid Cust ' || cnum); end if;
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if –then- elsif statement
IF <condition_1> THEN
statement-list-1
ELSIF <condition_2> THEN
statement-list-2
ELSIF <condition_n> THEN
statement-list-n
ELSE
statement-list-n+1
END IF;
if (score > 90) then na := na + 1;elsif (score > 80) then nb := nb + 1;elsif (score > 70) then nc := nc + 1;elsif (score > 60) then nd := nd + 1;else nf := nf + 1;end if;
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Exampole DECLARE
a NUMBER;
b NUMBER;
BEGIN
SELECT e,f INTO a,b FROM T1 WHERE e > 1;
IF b=1 THEN INSERT INTO T1 VALUES(b,a);
ELSE INSERT INTO T1 VALUES(b+10,a+10);
END IF;
END;
.
run;
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Loops
Loops are created with the following:
LOOP
<loop_body> /*A list of statements. */
END LOOP;
At least one of the statements in <loop_body> should be
an EXIT statement of the form EXIT WHEN <condition>;
The loop breaks if <condition> is true. For example, here is a
way to insert each of the pairs (1, 1) through (100, 100) into T1
of the above two examples:
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ExampleDECLARE
i NUMBER := 1;
BEGIN LOOP
INSERT INTO T1 VALUES(i, i);
i := i+1;
EXIT WHEN i>13;
END LOOP;
END;
.
run;
loop i := i + 1; if i > 10 then exit; end if; sum := sum + i;end loop;
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Other loop-forming statements EXIT by itself is an unconditional loop break. Use it
inside a conditional if you like.
A WHILE loop can be formed with
WHILE <condition> LOOP
<loop_body>
END LOOP;
A simple FOR loop can be formed with:
FOR <var> IN <start>..<finish>LOOP
<loop_body>
END LOOP;
Here, <var> can be any variable; it is local to the for
Loop and need not be declared. Also, <start> and
<finish> are constants.
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CursorsA cursor is a variable that runs through the tuples of some
relation.This relation can be a stored table, or it can be the answer to
somequery. By fetching into the cursor each tuple of the relation,
we canwrite a program to read and process the value of each such
tuple. Ifthe relation is stored, we can also update or delete the tuple at
thecurrent cursor position.
Cursor< cname> [ return <return-spec>] is <select statement>;Once a cursor has been declared, it can beproccessed using
open, fetch and close statements;Open <cname>;Fetch <cname> into < record | Variablrlist>;Close <cname>;
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The nest example illustrates a cursor loop. It uses
our example relation T1 (e,f) whose tuples are pairs of
integers. The program will delete every tuple whose first
component is less than the second, and insert the
reverse tuple into T1.
DECLARE
a T1.e%TYPE;
b T1.f%TYPE;
CURSOR T1 cursor IS
SELECT e, f FROM T1 WHERE e < f FOR UPDATE;
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BEGIN OPEN T1Cursor;
LOOP
FETCH T1Cursor INTO a, b;
EXIT WHEN T1Cursor%NOTFOUND;
DELETE FROM T1 WHERE CURRENT OF T1Cursor;
INSERT INTO T1 VALUES(b, a);
END LOOP;
CLOSE T1Cursor;
END;
.
run
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PL/SQL: CursorsCURSOR c1 RETURN customers%ROWTYPE IS select * from customers;CURSOR c2 IS select pno, pname, price*markdown sale_pricefrom parts;
_ Cursor c1 uses the RETURN clause which is consistent with the select list of the select statement in the SQL query associated with the cursor.
_ Cursor c2 uses a PL/SQL variable markdown in the select statement associated with the cursor.
Cursor attributes are %found, %notfound, %rowcount, %isopenExample:
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DECLARE CURSOR c1 IS select cno,cname,city from customers,zipcodes where customers.zip = zipcodes.zip; c1_rec c1%rowtype;BEGIN if not c1%isopen then open c1; end if; fetch c1 into c1_rec; while c1%found loop dbms_output.put_line('Row Number ' || c1%rowcount || '> ' || c1_rec.cno || ' ' || c1_rec.cname || ' ' || c1_rec.city); fetch c1 into c1_rec; end loop;close c1;END;
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Cursor for loop
DECLARECURSOR c1 ISselect cno,cname,cityfrom customers,zipcodeswhere customers.zip = zipcodes.zip;BEGIN for c1_rec in c1 loop dbms_output.put_line('Row Number ' || c1%rowcount || '> '
|| c1_rec.cno || ' ' || c1_rec.cname || ' ' || c1_rec.city); end loop;END; here we have implicit cursorsfor i in (select * from employees) loop......end loop;
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FunctionsDECLARE enum customers.cno%type; total number(10,2); status boolean; function total_emp_sales(emp_no IN employees.eno
%type) return number is sales number; begin select sum(price*qty) into sales from orders, odetails,
parts where orders.eno = emp_no and orders.ono =
odetails.ono and odetails.pno = parts.pno; return (sales); end;
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Example1
BEGINenum := 1000;total := total_emp_sales(enum);DBMS_OUTPUT.PUT_LINE('Total sales for
employee ' || enum || ' is ' || total);END;
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Stored Procedure and Functions CREATE [ or replace] procedure < proced_name>
[ (< parameter_list>)] as
<declarations>
BEGIN
<executable_section>
[ exception < exception_handler>]
END;
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Function (Example_1)create [ or replace] function < func_name>(<parameter_list>)
return <datatypr> as
<declarations>
begin
< executable section>
[exception
<exception_section>]
end;
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Function Example_2Create or replace function get_city(cname in
customers.cno%type)
return zipcodes.city%type as ccity zipcodes.city%type;
Begin
select city into ccity from customers, zipcodes
where cno = cnum and customers.zip = zipcodes.sip;
return (ccity);
End;
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Triggers
An SQL trigger is a mechanism that automatically executes a specified PL/SQL block ( triggers action) when a triggering event occurs on table. The triggering event may be one of
insert, delete or update.
The trigger is associated with DB table and is fired when the triggering event takes place on the table.
Triggers are created in Oracle using the
Create trigger statement whose syntax is
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Create Trigger(syntax)
create [or replace] trigger <trig_name> {before | after} { delete | insert | update[ of column [, column] …]} [ or { delete | insert | update[ of column [, column] …]}] … ON <table_name>[ [referencing { old [as] <old> [new [as] <new>] | new
[as]<new > [ old [as] <old> ]}]For each row[when (codition)]]PL/SQL_ blo ck
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Example
create or replace trigger update_price_of_parts
after update of price on parts
for each row
begin
insert into parts_log
values(:old.pno, user, sysdate, ; old.price, :new.price);
end;