PL/SQL - Oracle's Procedural Language Extension to SQL

8/14/2019 PL/SQL - Oracle's Procedural Language Extension to SQL

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PL/SQL


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PL/SQL - Oracle's ProceduralLanguage extension to SQL

4 loosely based on Ada4 includes (inter alia)

4 block structure4 datatypes (including Boolean)4 variables & constants4 assignment statement4 conditional statements

4 if .. then4 if .. then .. else4 if .. then .. elsif

4 loops4 basic loop (needs exit condition)4 for loop4 while loop

4 allows most SQL commands to be embedded


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Anonymous block examples

BEGIN DBMS_OUTPUT.PUT_LINE('Hello World!');END;

DECLARE v_day_of_week VARCHAR2(12); -- local variableBEGIN SELECT TO_CHAR(SYSDATE, 'Day') INTO v_day_of_week FROM sys.dual; IF v_day_of_week IN ('Saturday', 'Sunday') THEN -- note use of extra quote in string DBMS_OUTPUT.PUT_LINE('It''s the weekend!'); ELSE DBMS_OUTPUT.PUT_LINE('Too bad - it''ll be the weekend

soon'); END IF;END; SET SERVEROUTPUT ON

to get output fromDBMS_OUTPUT.PUT_LINE


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Stored programs

4Code stored in the database andexecuted on the server4advantages of DB approach

4 store once, use many4backup/recovery

4access control

4Multiple use by multiple

users/applications GRANT EXECUTE ON TO


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Stored procedure

CREATE OR REPLACE PROCEDURE TGITW IS v_day_of_week VARCHAR2(12); -- DECLARE not used hereBEGIN SELECT TO_CHAR(SYSDATE, 'Day') INTO v_day_of_week FROM sys.dual; IF v_day_of_week IN ('Saturday', 'Sunday') THEN DBMS_OUTPUT.PUT_LINE('It''s the weekend!'); ELSE DBMS_OUTPUT.PUT_LINE('Too bad - it''ll be the weekend soon'); END IF;END;

-- SQL*Plusexec TGITW

-- SQL*Plus and SQL DeveloperBEGIN TGITW;END;


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Stored function

CREATE OR REPLACE FUNCTION get_age(p_birth_date IN DATE) -- INput parameter RETURN INTEGER IS -- data type of result v_age INTEGER;BEGIN SELECT TRUNC(MONTHS_BETWEEN(SYSDATE, p_birth_date)/12) INTO v_age FROM sys.dual; RETURN(v_age); -- result of function

END;

GRANT EXECUTE ON get_age TO PUBLIC;

SELECT sname, bdate, brian.get_age(bdate) ageFROM rearp.studentORDER BY age DESC, bdate ASC;


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Also available

SELECT brian.valid_postcode('PL4 8AA')

FROM sys.dual;

TRUE

SELECT brian.valid_postcode('PL0 8AA')

FROM sys.dual;

FALSE


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Cursors

4 SQL query delivers an indivisible SET ofrows

4Cursor allows row by row processing of

the result set of a query4 Think of a cursor as a local table of

results4Read one record or row at a time4Do something with it

4


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Cursor operations

4DECLARE4specify query to populate cursor

4

OPEN4run query to populate cursor

4FETCH4

get a 'row' from the cursor4CLOSE


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DECLARE title_cur cursor

CURSOR title_cur IS

SELECT title

FROM books;4


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FETCH title_cur INTO v_title;

Serpent's Reach

Faded Sun, Kesrith, The

Faded Sun, Shon'jir, The

Titans, The

Black Tulip, The

Serpent's Reach

v_title


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Serpent's Reach



Titans, The

Black Tulip, The


v_title


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Serpent's Reach



Titans, The

Black Tulip, The


v_title


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Serpent's Reach



Titans, The

Black Tulip, The

Titans, The

v_title


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EXIT WHEN title_cur

%NOTFOUND;

Serpent's Reach



Titans, The

Black Tulip, The

v_title

No rows left in cursor


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Cursor example

DECLARE v_new_title VARCHAR2(60); v_title VARCHAR2(60); v_length INTEGER; v_char CHAR(1); CURSOR c_title IS SELECT title FROM books;BEGIN OPEN c_title; LOOP FETCH c_title INTO v_title; EXIT WHEN c_title%NOTFOUND; v_length := LENGTH(v_title); v_new_title := ''; FOR i IN 1..v_length LOOP v_char := SUBSTR(v_title, i, 1);

IF UPPER(v_char) IN ('A', 'E', 'I', 'O', 'U') THEN v_char := '*'; END IF; v_new_title := v_new_title||v_char; END LOOP; DBMS_OUTPUT.PUT_LINE(v_new_title); END LOOP; CLOSE c_title;

END;


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Listing stored code in

SQL Developer


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PL/SQL exception handling

4Enables bulletproofing of code tohandle run-time errors and retainprocessing control


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Example (modified from Oracledocumentation)

DECLARE v_pe_ratio NUMBER(3,1);BEGIN SELECT price / earnings -- potential division-by-zero

error INTO v_pe_ratio

FROM stocks WHERE symbol = 'XYZ'; INSERT INTO stats (symbol, ratio) VALUES ('XYZ', v_pe_ratio); COMMIT; EXCEPTION -- exception handlers begin WHEN ZERO_DIVIDE THEN -- handles 'division by zero' error

INSERT INTO stats (symbol, ratio) VALUES ('XYZ', NULL); COMMIT; WHEN OTHERS THEN -- handles all other errors ROLLBACK;END; -- exception handlers and block end here


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Database triggers revisited

4coded in PL/SQL

4critical for data integrity

4server-side integrity ensuresmore robust database than

client-side validation4

4


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Client-side integrity

databaseapplication

integrityche

cks

database is

vulnerable


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Issues

4Data sent to the server before beingchecked for integrity increasesnetwork traffic and server load

4 Perform simple client-side 'belt andbraces' integrity checking, e.g. checkfor required fields

4

Opaque server error messages need tobe communicated sensibly to theapplication/user


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Example trigger

CREATE OR REPLACE TRIGGER trg_clientsBEFORE INSERT OR UPDATE OF dob ON clients FOR EACH ROWBEGIN IF INSERTING THEN SELECT seq_client_id.nextval

INTO :NEW.client_id FROM sys.dual; END IF;IF MONTHS_BETWEEN(SYSDATE,:NEW.dob) < 18*12 THEN /* Issue error code (ORA-20000) and message */ RAISE_APPLICATION_ERROR(-20000, 'Client must be at

least 18 years of age'); END IF;END;4


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References

4PLSQL by Example on Portal

4

4

PL/SQL User's Guide andReference

4

Oracle10g Database ErrorMessages

4


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Exercise

4 Write a PL/SQL function (AVERAGE_PRICE) tocalculate the average retail price of books(rounded to the nearest penny) in theHarrington books table where the retail priceis above an amount specified as aparameter. You should use a cursor.

4 Test your results against

SELECTROUND(AVG(retail_price),2)

FROM books

Documents

PL/SQL - Oracle's Procedural Language Extension to SQL