sql pl sql essentials

8/6/2019 SQL Pl SQL Essentials

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SQL /PLSQL ESSENTIALS

Presenter :

Ranjeet Sharma


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What is SQL?

When a user wants to get some information

from a database file, he can issue a query.

A query is a userrequest to retrieve data

or information with a certain condition.

SQL is a query language that allows user tospecify the conditions.


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General StructureGeneral Structure

DISTINCT will eliminate duplication in the output

while ALL will keep all duplicated rows.

condition can be :

(1) an inequality, or

(2) a string comparison

using logical operators AND, OR, NOT.

SELECTSELECT [ALL / DISTINCT][ALL / DISTINCT] expr1expr1 [AS[AS col1col1],], expr2expr2[AS[AS col2col2]] ;;

FROMFROM tablenametablename WHEREWHERE conditioncondition


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GroupingGrouping

SELECT ...... FROM ...... WHERESELECT ...... FROM ...... WHEREconditioncondition ;;

GROUP BYGROUP BY groupexprgroupexpr [HAVING[HAVING requirementrequirement]]

Group functions:Group functions:

COUNT( ), SUM( ), AVG( ), MAX( ), MIN( )COUNT( ), SUM( ), AVG( ), MAX( ), MIN( )

groupexpr specifies the related rows to be grouped

as one entry. Usually it is a column.

WHERE condition specifies the condition of

individual rows before the rows are group.

HAVING requirement specifies the condition

involving the whole group.


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Natural JoinNatural Join

AA Natural JoinNatural Join is a join operation that joins twois a join operation that joins two

tables bytables by their common column. This operationtheir common column. This operation

is similar to the setting relation of two tables.is similar to the setting relation of two tables.

SELECT a.comcol, a.SELECT a.comcol, a.col1col1, b., b.col2col2,, expr1expr1,, expr2expr2 ;;

FROMFROM table1table1 a,a, table2table2b ;b ;

WHERE a.WHERE a.comcolcomcol= b.= b.comcolcomcol


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AnAn Outer JoinOuter Join is a join operation that includesis a join operation that includes

rows that have a match, plus rows that do notrows that have a match, plus rows that do not

have a match in the other table.have a match in the other table.

Outer JoinOuter Join


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Programming in Oracle

with PL/SQL

Procedural Language Extension to SQL


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PL/SQL Blocks PL/SQL code is built of Blocks, with a unique

structure.

There are two types of blocks in PL/SQL:

1. Anonymous Blocks: have no name (like scripts)

can be written and executed immediately in SQLPLUS

2. Named Blocks:

Procedures

Functions


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Anonymous Block Structure:

DECLARE (optional)/* Here you declare the variables you will use in this block */

BEGIN (mandatory)

/* Here you define the executable statements (what theblock DOES!)*/

EXCEPTION (optional)/* Here you define the actions that take place if an exception

is thrown during the run of this block */

END; (mandatory)/

Always put a new line with only a / at

the end of a block! (This tells Oracle

to run the block)

A correct completion of a block will

generate the following message:

PL/SQL procedure successfully

completed


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Creating a Cursor

We create a Cursor when we want to go over a resultof a query (like ResultSet in JDBC)

Syntax Example:

DECLAREcursor c is select * from sailors;

sailorData sailors%ROWTYPE;

BEGINopen c;

fetch c into sailorData;

sailorData is a

variable that canhold a ROW

from the sailors

table

Here the first

row of sailors is

inserted into

sailorData


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Explicit Cursor Attributes

Obtain status information about a cursor.

Attribute Type Description

%ISOPEN Boolean Evaluates to TRUE if the cursor

is open.

%NOTFOUND Boolean Evaluates to TRUE if the most

recent fetch does not return a row.

%FOUND Boolean Evaluates to TRUE if the most

recent fetch returns a row;

complement of %NOTFOUND

%ROWCOUNT Number Evaluates to the total number of

rows returned so far.


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Loops: Simple Loop

DECLARE

i number_table.num%TYPE := 1;BEGINLOOPINSERT INTO number_tableVALUES(i);i := i + 1;EXIT WHEN i > 10;

END LOOP;END;

create table number_table(

num NUMBER(10));


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Loops: Simple Cursor Loop

DECLARE

cursor c is select * from number_table;cVal c%ROWTYPE;BEGINopen c;LOOP

fetch c into cVal;EXIT WHEN c%NOTFOUND;insert into doubles values(cVal.num*2);

END LOOP;END;

create table number_table(

num NUMBER(10));


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Printing Output

You need to use a function in the DBMS_OUTPUT

package in order to print to the output

If you want to see the output on the screen, you must

type the following (before starting):

set serveroutput on format wrapped size 1000000

Then print using

dbms_output. put_line(your_string);

dbms_output.put(your_string);


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Trapping Exceptions

Here we define the actions that should happen

when an exception is thrown.

Example Exceptions:

NO_DATA_FOUND

TOO_MANY_ROWS

ZERO_DIVIDE


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DECLAREnum_row number_table%ROWTYPE;

BEGINselect *

into num_rowfrom number_table;dbms_output.put_line(1/num_row.num);

EXCEPTIONWHENNO_DATA_FOUND THEN

dbms_output.put_line('No data!');

WHEN TOO_MANY_ROWS THENdbms_output.put_line('Too many!');WHEN OTHERS THEN

dbms_output.put_line(Error);end;


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User-Defined ExceptionDECLARE

e_number1 EXCEPTION;cnt NUMBER;

BEGINselect count(*)into cnt

from number_table;

IF cnt = 1 THEN RAISE e_number1;ELSE dbms_output.put_line(cnt);END IF;

EXCEPTIONWHEN e_number1 THEN

dbms_output.put_line('Count = 1');

end;


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Functions and Procedures

Up until now, our code was in an anonymousblock

It was run immediately

It is useful to put code in a function orprocedure so it can be called several times

Once we create a procedure or function in a

Database, it will remain until deleted (like atable).


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Creating a Function

Almost exactly like creating a procedure, but

you supply a return type

CREATE [OR REPLACE] FUNCTIONfunction_name

[(parameter1 [mode1] datatype1,parameter2[mode2] datatype2,

. . .)]RETURN datatypeIS|ASPL/SQL Block;


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Triggers

Triggers are special procedures which we wantactivated when someone has performed someaction on the DB.

For example, we might define a trigger that isexecuted when someone attempts to insert arow into a table, and the trigger checks thatthe inserted data is valid.


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Trigger types

1) Row level trigger - An event is triggered for

each row upated, inserted or deleted.

2) Statement level trigger - An event is

triggered for each sql statement executed.


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Trigger Syntax

CREATE [OR REPLACE ] TRIGGER trigger_name{BEFORE | AFTER } {INSERT [OR] | UPDATE [OR] |DELETE}

[OF col_name] ON table_name [REFERENCING OLD AS o NEW AS n]

[FOR EACH ROW] WHEN (condition)

BEGIN

--- sql statements

END;


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1) BEFORE UPDATE, Statement Level: This triggerwill insert a record into the table 'product_check'before a sql update statement is executed, at the

statement level.

CREATEorREPLACE TRIGGERBefore_Update_Stat_productBEFOREUPDATE

ONproduct Begin INSERT INTO product_check

Values('Beforeupdate,statementlevel',sysdate);

END; /


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2) BEFORE UPDATE, Row Level: This trigger willinsert a record into the table 'product_check'

before each row is updated.

CREATEorREPLACE TRIGGERBefore_Upddate_Row_productBEFOREUPDATEONproductFOR EACH ROW

BEGIN

INSERT INTO product_check Values('Before

update rowlevel',sysdate); END;

/


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PL/SQL in Web Applications

mod_plsql :Plug in to Oracle HTTP Server, an

implementation of pl sql gateway

mod_plsql maps Web client requests to

PL/SQL stored subprograms over HTTP


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MOD_PLSQL was formerly called the Oracle PL/SQL Cartridge and OWA

(Oracle Web Agent).

mod_plsql maps Web client requests to PL/SQL stored subprograms over HTTP

The mod_plsql plug-in enables you to use PL/SQL stored subprograms to

process HTTP requests and generate responses

Obtain info of http requestGenerates HTTP Headers

And Browser cookies

invoke a PL/SQL storedsubprogram through an

HTTP listener


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CREATE OR REPLACE PROCEDURE print_employees IS CURSOR emp_cursor IS

SELECT last_name, first_name

FROM hr.employees

ORDER BY last_name;

BEGIN HTP.PRINT('');

HTP.PRINT('');

HTP.PRINT('');

HTP.PRINT('List of Employees');

HTP.PRINT('');

HTP.PRINT('');

HTP.PRINT('List of Employees');

HTP.PRINT('');

HTP.PRINT('');

HTP.PRINT('Last Name');

HTP.PRINT('First Name');

HTP.PRINT('');

FOR emp_record IN emp_cursor LOOP

HTP.PRINT('');

HTP.PRINT('' || emp_record.last_name || '');

HTP.PRINT('' || emp_record.first_name || '');

END LOOP; HTP.PRINT('');

HTP.PRINT('');

HTP.PRINT('');

END;


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http://host:port/plsql/print_employees

http://example.

com:8080/plsql/print_employees

The Web browser returns an HTML page with

a table that includes the first and last name of

every employee in the hr.employees table.


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