sql function

sql function

1 "'
2 ||
3 isql*plus  http://127.0.00.1/isqlplus
4 desc author
5 initcap('SQL Course')
  INSERT('JellwWord','W')  6
   LPAD (salary,10,'*')  *****24000
   RPAD (salary,10,'*')  24000*****
   TRIM ('H' from 'HolloWorld') olloWord
   substr('helloword',1,5)  hello
   substr('helloword',-1,5) oword
6  Number Functions
   round(45.926,2)   45.93
   round(45.926,-2) 0
   round(55.926,-2) 100
   trunc(45.926,2)   45.92
   mod(1600,300)  100
7 data function
   systdate
   (sysdate-hire_date)/7 as weeks
   months_between  number of months between two dates
   months_between ('01-sep-95','11,jan-94')  19.6774194
   add_months      add calendar months to date
   add_months('11-JAN-94',6)  '11-JUL-94'
   next_day        next day of the date specified
   next_day('01-SEP-95','FRIDAY') '08-SEP-95'
   last_day        last day of the month
   last_day('01-feb-95')  '28-feb-95'
   round           round date
   assume sysdate='25-jul-95'
   round(sysdate,'month') 01-aug-95
   round(sysdate,'year')  01-JAN-96
   trunc           truncate date
   trunc(sysdate,'month') 01-Jul-95
   trunc(sysdate,'month') 01-JAN-95
8  Conversion Functions 
  1) implicit data typ conversion
   varchar2 or char  ---number
   varchar2 or char  ---date
   numbeer           ---varchar2
   date              ---varchar2
  2) to_char(date,'format')
  format:
    YYYY Full year in numbers
    YEAR Year spelled out
    MM   Two-digit value for month
    MONTH Full name of the month
    MON  THree-letter abbreviation of the month
    DY   Three-letter abbreviation of the day of the week
    DAY  Full name of the day of hte week
    DD   Numberic day of the month
    HH24:MI:SS AM  15:45:32:PM
    DD "of"  MONTH 12 of october
  3) to_char function with number 
   TO_CAHR(number,'format_model')
   These are some of the format elements you can use with the to_char function to display number as a character.
    9 Reqresents a number
    0 Forces a zero to be displayed
    $ Places a flationg dollar sign
    L Uses the floating local currency symbol
    . Prints a decimal point
    , Print a thousand director
  select to_char(qtym,"$999.99")
  4) Using t_number and to _date functions
   a converting a character string to a number format using to_number function
   to_number(char,"format")l
   b converting a character string to a date format
   to_date(char,"format")
5 Nesting Functions
.Single-row function can be nested to many level
.Nested function can be evaluated from deepest level
6General Function
These function work with any data type and pertain to using nulls
nvl(expr1,expr2);
nvl2(expr1,expr2,expr3)
nullif(expr1,expr2)
coalesce(expr1,expr2,,,,exprn)
 1) nvl function
 convert a null to an actual function
 a Data type can be used are data character and number
 b Data types must match                              
 (set wrap off
  set line 1000
 )
 2)Using the COALESCE Function
 a The advantage of the coalesce function over nal function is that coalesce function can take multiple alternative value
 b If the first value is not null, it return that expression,otherwise,it does a coalesce of remaining expressions
6 Conditional Expressions
 a Provide the use of if-then-else logic
 b use two methods: case expression decode function
  select last_name,job_id,salary,
         case job_id when 'it' then 1*salary
                      when 'manager' then 1.2*salary
         else salary end;
  from employee.

  select last_namek,job_id,salary,
         decode(job_id,'it' ,1*salary,
                        'manager',1.2*salary,
                salary)
   from employees