TRIPATHI SHIVANAND BLOG: Oracle Sql Part3

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DATE FUNCTIONS

Oracle default date format is DD-MON-YY.

We can change the default format to our desired format by using the following command.

SQL> alter session set nls_date_format = ‘DD-MONTH-YYYY’;

But this will expire once the session was closed.

a) SYSDATE

This will give the current date and time.

Ex:

SQL> select sysdate from dual;

SYSDATE

-----------

24-DEC-06

b) CURRENT_DATE

This will returns the current date in the session’s timezone.

Ex:

SQL> select current_date from dual;

CURRENT_DATE

------------------

24-DEC-06

c) CURRENT_TIMESTAMP

This will returns the current timestamp with the active time zone information.

Ex:

SQL> select current_timestamp from dual;

CURRENT_TIMESTAMP

---------------------------------------------------------------------------

24-DEC-06 03.42.41.383369 AM +05:30

d) SYSTIMESTAMP

This will returns the system date, including fractional seconds and time zone of the

database.

Ex:

SQL> select systimestamp from dual;

SYSTIMESTAMP

---------------------------------------------------------------------------

24-DEC-06 03.49.31.830099 AM +05:30

e) LOCALTIMESTAMP

This will returns local timestamp in the active time zone information, with no time

zone information shown.

Ex:

SQL> select localtimestamp from dual;

LOCALTIMESTAMP

---------------------------------------------------------------------------

24-DEC-06 03.44.18.502874 AM

f) DBTIMEZONE

This will returns the current database time zone in UTC format. (Coordinated Universal

Time)

Ex:

SQL> select dbtimezone from dual;

DBTIMEZONE

---------------

-07:00

g) SESSIONTIMEZONE

This will returns the value of the current session’s time zone.

Ex:

SQL> select sessiontimezone from dual;

SESSIONTIMEZONE

------------------------------------

+05:30

h) TO_CHAR

This will be used to extract various date formats.

The available date formats as follows.

Syntax: to_char (date, format)

Ex:

SQL> select to_char(sysdate,'dd month yyyy hh:mi:ss am dy') from dual;

TO_CHAR(SYSDATE,'DD MONTH YYYYHH:MI

----------------------------------------------------

24 december 2006 02:03:23 pm sun

SQL> select to_char(sysdate,'dd month year') from dual;

TO_CHAR(SYSDATE,'DDMONTHYEAR')

-------------------------------------------------------

24 december two thousand six

SQL> select to_char(sysdate,'dd fmmonth year') from dual;

TO_CHAR(SYSDATE,'DD FMMONTH YEAR')

-------------------------------------------------------

24 december two thousand six

SQL> select to_char(sysdate,'ddth DDTH') from dual;

TO_CHAR(S

------------

24th 24^TH

SQL> select to_char(sysdate,'ddspth DDSPTH') from dual;

TO_CHAR(SYSDATE,'DDSPTHDDSPTH

------------------------------------------

twenty-fourth TWENTY-FOURTH

SQL> select to_char(sysdate,'ddsp Ddsp DDSP ') from dual;

TO_CHAR(SYSDATE,'DDSPDDSPDDSP')

------------------------------------------------

twenty-four Twenty-Four TWENTY-FOUR

i) TO_DATE

This will be used to convert the string into data format.

Syntax: to_date (date)

Ex:

SQL> select to_char(to_date('24/dec/2006','dd/mon/yyyy'), 'dd * month * day')

from dual;

TO_CHAR(TO_DATE('24/DEC/20

--------------------------

24 * december * Sunday

-- If you are not using to_char oracle will display output in default date format.

j) ADD_MONTHS

This will add the specified months to the given date.

Syntax: add_months (date, no_of_months)

Ex:

SQL> select add_months(to_date('11-jan-1990','dd-mon-yyyy'), 5) from dual;

ADD_MONTHS

----------------

11-JUN-90

SQL> select add_months(to_date('11-jan-1990','dd-mon-yyyy'), -5) from dual;

ADD_MONTH

---------------

11-AUG-89

Ø If no_of_months is zero then it will display the same date.

Ø If no_of_months is null then it will display nothing.

k) MONTHS_BETWEEN

This will give difference of months between two dates.

Syntax: months_between (date1, date2)

Ex:

SQL> select months_between(to_date('11-aug-1990','dd-mon-yyyy'), to_date('11-

jan-1990','dd-mon-yyyy')) from dual;

MONTHS_BETWEEN(TO_DATE('11-AUG-1990','DD-MON-YYYY'),TO_DATE('11-JAN-1990','DD-MON-YYYY'))

-----------------------------------------------------------------------------------------

SQL> select months_between(to_date('11-jan-1990','dd-mon-yyyy'), to_date('11-

aug-1990','dd-mon-yyyy')) from dual;

MONTHS_BETWEEN(TO_DATE('11-JAN-1990','DD-MON-YYYY'),TO_DATE('11-AUG-1990','DD-MON-YYYY'))

--------------------------------------------------------------------------------------

-7

l) NEXT_DAY

This will produce next day of the given day from the specified date.

Syntax: next_day (date, day)

Ex:

SQL> select next_day(to_date('24-dec-2006','dd-mon-yyyy'),'sun') from dual;

NEXT_DAY(

-------------

31-DEC-06

-- If the day parameter is null then it will display nothing.

m) LAST_DAY

This will produce last day of the given date.

Syntax: last_day (date)

Ex:

SQL> select last_day(to_date('24-dec-2006','dd-mon-yyyy'),'sun') from dual;

LAST_DAY(

-------------

31-DEC-06

n) EXTRACT

This is used to extract a portion of the date value.

Ex:

SQL> select extract(year from sysdate) from dual;

EXTRACT(YEARFROMSYSDATE)

------------------------------------

2006

-- You can extract only one value at a time.

o) GREATEST

This will give the greatest date.

Syntax: greatest (date1, date2, date3 … daten)

Ex:

SQL> select greatest(to_date('11-jan-90','dd-mon-yy'),to_date('11-mar-90','dd-

mon-yy'),to_date('11-apr-90','dd-mon-yy')) from dual;

GREATEST(

-------------

11-APR-90

p) LEAST

This will give the least date.

Syntax: least (date1, date2, date3 … daten)

Ex:

SQL> select least(to_date('11-jan-90','dd-mon-yy'),to_date('11-mar-90','dd-mon-

yy'),to_date('11-apr-90','dd-mon-yy')) from dual;

LEAST(

-------------

11-JAN-90

q) ROUND

Round will rounds the date to which it was equal to or greater than the given date.

Syntax: round (date, (day | month | year))

If the second parameter was year then round will checks the month of the given date in

the following ranges.

JAN -- JUN

JUL -- DEC

If the month falls between JAN and JUN then it returns the first day of the current year.

If the month falls between JUL and DEC then it returns the first day of the next year.

If the second parameter was month then round will checks the day of the given date in

the following ranges.

1 -- 15

16 -- 31

If the day falls between 1 and 15 then it returns the first day of the current month.

If the day falls between 16 and 31 then it returns the first day of the next month.

If the second parameter was day then round will checks the week day of the given date

in the following ranges.

SUN -- WED

THU -- SUN

If the week day falls between SUN and WED then it returns the previous sunday.

If the weekday falls between THU and SUN then it returns the next sunday.

Ø If the second parameter was null then it returns nothing.

SQL> select round(to_date('24-dec-04','dd-mon-yy'),'year'), round(to_date('11-mar-

06','dd-mon-yy'),'year') from dual;

ROUND(TO_ ROUND(TO_

------------ ---------------

01-JAN-05 01-JAN-06

SQL> select round(to_date('11-jan-04','dd-mon-yy'),'month'), round(to_date('18-

jan-04','dd-mon-yy'),'month') from dual;

ROUND(TO_ ROUND(TO_

------------- ---------------

01-JAN-04 01-FEB-04

SQL> select round(to_date('26-dec-06','dd-mon-yy'),'day'), round(to_date('29-dec-

06','dd-mon-yy'),'day') from dual;

ROUND(TO_ ROUND(TO_

-------------- --------------

24-DEC-06 31-DEC-06

SQL> select to_char(round(to_date('24-dec-06','dd-mon-yy')), 'dd mon yyyy

hh:mi:ss am') from dual;

TO_CHAR(ROUND(TO_DATE('

---------------------------------

24 dec 2006 12:00:00 am

r) TRUNC

Trunc will chops off the date to which it was equal to or less than the given date.

Syntax: trunc (date, (day | month | year))

Ø If the second parameter was year then it always returns the first day of the current year.

Ø If the second parameter was month then it always returns the first day of the current month

Ex:

SQL> select trunc(to_date('24-dec-04','dd-mon-yy'),'year'), trunc(to_date('11-mar-

06','dd-mon-yy'),'year') from dual;

TRUNC(TO_ TRUNC(TO_

------------- --------------

01-JAN-04 01-JAN-06

SQL> select trunc(to_date('11-jan-04','dd-mon-yy'),'month'), trunc(to_date('18-jan-

04','dd-mon-yy'),'month') from dual;

TRUNC(TO_ TRUNC(TO_

------------- -------------

01-JAN-04 01-JAN-04

SQL> select trunc(to_date('26-dec-06','dd-mon-yy'),'day'), trunc(to_date('29-dec-

06','dd-mon-yy'),'day') from dual;

TRUNC(TO_ TRUNC(TO_

------------- --------------

24-DEC-06 24-DEC-06

SQL> select to_char(trunc(to_date('24-dec-06','dd-mon-yy')), 'dd mon yyyy hh:mi:ss

am') from dual;

TO_CHAR(TRUNC(TO_DATE('

---------------------------------

24 dec 2006 12:00:00 am

s) NEW_TIME

This will give the desired timezone’s date and time.

Syntax: new_time (date, current_timezone, desired_timezone)

Available timezones are as follows.

Ex:

SQL> select to_char(new_time(sysdate,'gmt','yst'),'dd mon yyyy hh:mi:ss am') from

dual;

TO_CHAR(NEW_TIME(SYSDAT

-----------------------------------

24 dec 2006 02:51:20 pm

SQL> select to_char(new_time(sysdate,'gmt','est'),'dd mon yyyy hh:mi:ss am') from

dual;

TO_CHAR(NEW_TIME(SYSDAT

-----------------------

24 dec 2006 06:51:26 pm

t) COALESCE

This will give the first non-null date.

Syntax: coalesce (date1, date2, date3 … daten)

Ex:

SQL> select coalesce('12-jan-90','13-jan-99'), coalesce(null,'12-jan-90','23-mar-

98',null) from dual;

COALESCE( COALESCE(

------------- ------------

12-jan-90 12-jan-90

MISCELLANEOUS FUNCTIONS

Ø Uid

Ø User

Ø Vsize

Ø Rank

Ø Dense_rank

a) UID

This will returns the integer value corresponding to the user currently logged in.

Ex:

SQL> select uid from dual;

UID

----------

319

b) USER

This will returns the login’s user name.

Ex:

SQL> select user from dual;

USER

----------------

SAKETH

c) VSIZE

This will returns the number of bytes in the expression.

Ex:

SQL> select vsize(123), vsize('computer'), vsize('12-jan-90') from dual;

VSIZE(123) VSIZE('COMPUTER') VSIZE('12-JAN-90')

------------- ----------------------- ----------------------

3 8 9

d) RANK

This will give the non-sequential ranking.

Ex:

SQL> select rownum,sal from (select sal from emp order by sal desc);

ROWNUM SAL

---------- ----------

1 5000

2 3000

3 3000

4 2975

5 2850

SQL> select rank(2975) within group(order by sal desc) from emp;

RANK(2975)WITHINGROUP(ORDERBYSALDESC)

---------------------------------------------------------

d) DENSE_RANK

This will give the sequential ranking.

Ex:

SQL> select dense_rank(2975) within group(order by sal desc) from emp;

DENSE_RANK(2975)WITHINGROUP(ORDERBYSALDESC)

-----------------------------------------------------------------

CONVERSION FUNCTIONS

a) BIN_TO_NUM

This will convert the binary value to its numerical equivalent.

Syntax: bin_to_num( binary_bits)

Ex:

SQL> select bin_to_num(1,1,0) from dual;

BIN_TO_NUM(1,1,0)

------------------------

Ø If all the bits are zero then it produces zero.

Ø If all the bits are null then it produces an error.

b) CHARTOROWID

This will convert a character string to act like an internal oracle row identifier or rowid.

c) ROWIDTOCHAR

This will convert an internal oracle row identifier or rowid to character string.

d) TO_NUMBER

This will convert a char or varchar to number.

e) TO_CHAR

This will convert a number or date to character string.

f) TO_DATE

This will convert a number, char or varchar to a date.

ROLLUP GROUPING CUBE

These are the enhancements to the group by feature.

USING ROLLUP

This will give the salaries in each department in each job category along wih the total salary for individual departments and the total salary of all the departments.

SQL> Select deptno,job,sum(sal) from emp group by rollup(deptno,job);

DEPTNO JOB SUM(SAL)

---------- --------- ----------

10 CLERK

USING GROUPING

In the above query it will give the total salary of the individual departments but with a

blank in the job column and gives the total salary of all the departments with blanks in

deptno and job columns.

To replace these blanks with your desired string grouping will be used

SQL> select decode(grouping(deptno),1,'All Depts',deptno),decode(grouping(job),1,'All

jobs',job),sum(sal) from emp group by rollup(deptno,job);

DECODE(GROUPING(DEPTNO),1,'ALLDEPTS',DEP DECODE(GR SUM(SAL)

----------------------------------- ---------------------------------- --------------

10 CLERK 1300

10 MANAGER 2450

bs 29025

Grouping will return 1 if the column which is specified in the grouping function has been

used in rollup.

Grouping will be used in association with decode.

USING CUBE

This will give the salaries in each department in each job category, the total salary for individual departments, the total salary of all the departments and the salaries in each job category.

SQL> select decode(grouping(deptno),1,’All Depts’,deptno),decode(grouping(job),1,’All

Jobs’,job),sum(sal) from emp group by cube(deptno,job);

DECODE(GROUPING(DEPTNO),1,'ALLDEPTS',DEP DECODE(GR SUM(SAL)

----------------------------------- ------------------------------------ ------------

10 CLERK 1300

10 MANAGER 2450

VIEWS

A view is a database object that is a logical representation of a table. It is delivered from a table but has no storage of its own and often may be used in the same manner as a table.

A view takes the output of the query and treats it as a table, therefore a view can be thought of as a stored query or a virtual table.

TYPES

Ø Simple view

Ø Complex view

VIEWS WITH DML

Ø View with not null column -- insert with out not null column not possible

-- update not null column to null is not possible

-- delete possible

Ø View with out not null column which was in base table -- insert not possible

-- update, delete possible

Ø View with expression -- insert , update not possible

-- delete possibles)

CREATING VIEW WITHOUT HAVING THE BASE TABLE

SQL> Create force view stud as select *From student;

-- Once the base table was created then the view is validated.

VIEW WITH CHECK OPTION CONSTRAINT

SQL> Create view stud as select *from student where marks = 500 with check option

constraint Ck;

- Insert possible with marks value as 500

- Update possible excluding marks column

- Delete possible

DROPPING VIEWS

SQL> drop view dept_v

SYNONYM AND SEQUENCE

SYNONYM

A synonym is a database object, which is used as an alias for a table, view or sequence.

TYPES

Ø Private

Ø Public

Private synonym is available to the particular user who creates.

Public synonym is created by DBA which is available to all the users

CREATE AND DROP

SQL> create synonym s1 for emp;

SQL> create public synonym s2 for emp;

SQL> drop synonym s1;

SEQUENCE

A sequence is a database object, which can generate unique, sequential integer values.

It can be used to automatically generate primary key or unique key values.

A sequence can be either in an ascending or descending order.

Syntax:

Create sequence <seq_name> [increment bty n] [start with n] [maxvalue n]

[minvalue n] [cycle/nocycle] [cache/nocache];

By defalult the sequence starts with 1, increments by 1 with minvalue of 1 and with nocycle, nocache.

Cache option pre-alloocates a set of sequence numbers and retains them in memory for faster access.

Ex:

SQL> create sequence s;

SQL> create sequence s increment by 10 start with 100 minvalue 5 maxvalue 200 cycle

cache 20;

USING SEQUENCE

SQL> create table student(no number(2),name varchar(10));

SQL> insert into student values(s.nextval, ‘saketh’);

Ø Initially currval is not defined and nextval is starting value.

Ø After that nextval and currval are always equal.

CREATING ALPHA-NUMERIC SEQUENCE

SQL> create sequence s start with 111234;

SQL> Insert into student values (s.nextval || translate

(s.nextval,’1234567890’,’abcdefghij’));

ALTERING SEQUENCE

We can alter the sequence to perform the following.

Ø Set or eliminate minvalue or maxvalue.

Ø Change the increment value.

Ø Change the number of cached sequence numbers.

Ex:

SQL> alter sequence s minvalue 5;

SQL> alter sequence s increment by 2;

SQL> alter sequence s cache 10;

DROPPING SEQUENCE

SQL> drop sequence s;

JOINS

Ø The purpose of a join is to combine the data across tables.

Ø A join is actually performed by the where clause which combines the specified rows of tables.

Ø If a join involves in more than two tables then oracle joins first two tables based on the joins condition and then compares the result with the next table and so on.

TYPE

Assume that we have the following tables.

SQL> select * from dept;

DEPTNO DNAME LOC

------ ---------- ----------

10 mkt hyd

SQL> select * from emp

EMPNO ENAME JOB MGR DEPTNO

---------- ---------- ---------- ---------- ----------

111 saketh analyst 444 10

222 sudha clerk 333 20

EQUI JOIN

A join which contains an ‘=’ operator in the joins condition.

SQL> select empno,ename,job,dname,loc from emp e,dept d where e.deptno=d.deptno;

EMPNO ENAME JOB DNAME LOC

---------- ---------- ---------- ---------- ----------

111 saketh analyst mkt hy

USING CLAUSE

SQL> select empno,ename,job ,dname,loc from emp e join dept d using(deptno);

EMPNO ENAME JOB DNAME LOC

---------- ---------- ---------- ---------- ----------

111 saketh analyst mkt hy

ON CLAUSE

SQL> select empno,ename,job,dname,loc from emp e join dept d on(e.deptno=d.deptno);

EMPNO ENAME JOB DNAME LOC

---------- ---------- ---------- ---------- ----------

111 saketh analyst mkt hyd

NON-EQUI JOIN

A join which contains an operator other than ‘=’ in the joins condition.

Ex:

SQL> select empno,ename,job,dname,loc from emp e,dept d where e.deptno >

d.deptno;

EMPNO ENAME JOB DNAME LOC

---------- ---------- ---------- ---------- ----------

222 sudha clerk mkt hyd

444 madhu engineer mkt hy

SELF JOIN

Joining the table itself is called self join.

Ex:

SQL> select e1.empno,e2.ename,e1.job,e2.deptno from emp e1,emp e2 where

e1.empno=e2.mgr;

EMPNO ENAME JOB DEPTNO

---------- ---------- ---------- ----------

111 jagan analyst 10

222 madhu clerk 4

NATURAL JOIN

Natural join compares all the common columns.

Ex:

SQL> select empno,ename,job,dname,loc from emp natural join dept;

EMPNO ENAME JOB DNAME LOC

---------- ---------- ---------- ---------- ----------

111 saketh analyst mkt hyd

CROSS JOIN

This will gives the cross produc

SQL> select empno,ename,job,dname,loc from emp cross join dept;

EMPNO ENAME JOB DNAME LOC

---------- ---------- ---------- ---------- ----------

111 saketh analyst mkt hy

OUTER JOIN

Outer join gives the non-matching records along with matching records.

LEFT OUTER JOIN

This will display the all matching records and the records which are in left hand side table those that are not in right hand side table.

Ex:

SQL> select empno,ename,job,dname,loc from emp e left outer join dept d

on(e.deptno=d.deptno);

SQL> select empno,ename,job,dname,loc from emp e,dept d where

e.deptno=d.deptno(+);

EMPNO ENAME JOB DNAME LOC

---------- ---------- ---------- ---------- ----------

RIGHT OUTER JOIN

This will display the all matching records and the records which are in right hand side table those that are not in left hand side table.

Ex:

SQL> select empno,ename,job,dname,loc from emp e right outer join dept d

on(e.deptno=d.deptno);

SQL> select empno,ename,job,dname,loc from emp e,dept d where e.deptno(+) =

d.deptno

EMPNO ENAME JOB DNAME LOC

---------- ---------- ---------- ---------- ----------

FULL OUTER JOIN

This will display the all matching records and the non-matching records from both tables.

Ex:

SQL> select empno,ename,job,dname,loc from emp e full outer join dept d

on(e.deptno=d.deptno);

EMPNO ENAME JOB DNAME LO

INNER JOIN

This will display all the records that have matc

Ex:

SQL> select empno,ename,job,dname,loc from emp inner join dept using(deptno);

EMPNO ENAME JOB DNAME LOC

---------- ---------- ---------- ---------- ----------

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