What is a function?
A function is similar to an operator in operation. A function is a name that performs a specific task. A function may or may not take values (arguments) but it always returns a value as the result. If function takes values then these values are to be given within parentheses after the function name. The following is the general format of a function.
function [(argument1, argument2,...) ]
If the function doesn’t take any value then function name can be used alone and even parentheses are not required.
Types of functions
Functions are classified based on the type of data on which they perform the operation. The following are the different types of functions available in Oracle.
Arithmetic Functions.
Date & Time functions.
String functions.
Conversion functions.
Miscellaneous functions.
Group functions.
Arithmetic functions perform take numeric data; date functions take date type data and string functions take strings. Conversion functions are used to convert the given value from one type to another. Miscellaneous functions perform operations on any type of data. Group functions are used to perform operations on the groups created by GROUP BY clause.
Note: Group functions or aggregate functions perform their operation on a group (a collection of rows). All the remaining functions are called as singlerow functions as they return a result for each row.
Arithmetic Functions
Arithmetic functions take numbers and perform arithmetic operations. Table 1 lists the arithmetic functions available in Oracle.
Function Description
ABS(value) Absolute value of the given value.
CEIL(value) Smallest integer larger than or equal to value
FLOOR(value) Largest integer smaller than or equal to value
MOD(value,divisor) Remainder of the division between the value and divisor.
POWER(value,exponent) Value is raised to exponent.
ROUND(value[,precision]) Rounds value to precision. Precision can be negative if rounding is to be done on the left of the decimal point.
TRUNC(value[,precision]) Truncates instead of rounding. Otherwise same as ROUND.
SQRT(value) Square root of value.
SIGN(value) Returns 1 if value > 0, 1 if value <0, 0 if value = 0
Table 1: Arithmetic Functions.
The following are a few examples of arithmetic functions.
select mod(10,4) from dual;
The above command displays 2 as the result as the remainder of the division between 10 and 4 is 2.
ROUND and TRUNC functions
ROUND and TRUNC functions are used to round and truncate the given number to the given number of digits (either on the right or left of the decimal point). ROUND takes the leftmost digit that is being lost and accordingly adds one to the rightmost digit. TRUNC doesn’t take the leftmost digit into account. It just truncates the given number to the given precision.
select round(1047.785,2), trunc(1047.785,2) from dual;
The above command will display 1047.79 and 1047.78. This is because TRUNC doesn’t take the digits being lost into account.
The following examples illustrate the result of ROUND and TRUNC functions with positive and negative precision.
Function Result
ROUND(1295.356,2) 1295.36
TRUNC(1295.356,2) 1295.35
ROUND(1295.356,0) 1295
ROUND(1285.356, 1) 1290
TRUNC(1285.356, 1) 1280
ROUND(1295,2) 1300
When precision in ROUND is positive then rounding takes place to the specified number of digits on the right of decimal point. For example, if precision is 2 it means round number to 2 digits on the right of the decimal point. When precision is negative; it means number is to be rounded to the left of the decimal point. In both the cases if the leftmost digit of the digits being lost is >= 5 then one is added to the rightmost digit of the digits that are retained.
In the example given above, ROUND (1285.356, 1) will result in 1290. Because one digit on the left of decimal point is to be set to zero, means 5 is replaced with 0. As the digit that is replaced with zero (5 in this case) is >= 5 one is added to digit on the left of it (8) to make it 9. So the result is 1290.
ROUND (1295,2) results in 1300. This is because in 1295 two digits on the left of decimal point are set to zeroes( 1200) and as leftmost digit out of digits that are set to zero is 9 one is added to 2, which is the rightmost digit in the remaining portion. This makes it 1300.
Note: ROUND and TRUNC functions can also be used with date data type. More on this later in this chapter.
CEIL & FLOOR functions
CEIL produces the smallest integer that is greater than or equal to the given value. Whereas FLOOR is opposite of CEIL. The following table illustrates the usage of these two related functions.
Function Result
CEIL(1.3) 2
CEIL(2) 2
CEIL(2.3) 2
FLOOR(1.3) 1
FLOOR(2) 2
FLOOR(2.3) 3
DUAL Table
This is a table that is made available to every account in Oracle database. This table contains one row and one column. This table can be used with SELECT when result of the expression is to be displayed only for once.
SQL> describe dual
Name Null? Type
  
DUMMY VARCHAR2(1)
For example, to display the current system date the following SELECT can be used:
SQL> select sysdate from dual;
SYSDATE

24AUG01
As DUAL table contains only one row, the result is displayed only for once.
The following example displays the course fee by rounding it to thousands.
select ccode,name, round(fee,3) “fee”
from courses;
CCODE NAME fee
  
ora Oracle database 5000
vbnet VB.NET 6000
c C programming 4000
asp ASP.NET 5000
java Java Language 5000
xml XML Programming 4000
Scientific functions
The following are the other arithmetic functions that are rarely used in business applications. They are mainly used in scientific applications. However as they are available in Oracle, we will get to know them.
Function Description
ACOS(value) Arc cosine of the given value. The value is in the range –1 to 1 and return value is in radians.
ASIN(value) Arc sine of the value.
ATAN(value) Arc tangent of the value.
COS(value) Cosine of the value.
COSH(value) Hyperbolic cosine of the value.
EXP(value) Return e (2.71828183) raised to value power.
LN(value) Natural logarithm of value.
LOG(base,value) Logarithm with base of value.
SIN(value) Sine of the value.
SINH(value) Hyperbolic sine of the value.
TAN(value) Tangent of the value.
TANH(value) Hyperbolic tangent of the value.
Table 2: Scientific Functions.
The following are few examples of these scientific functions.
select exp(2) from dual;
EXP(2)

7.3890561
select log(10,10) from dual
LOG(10,10)

1
SELECT COS(180 * 3.14159265359/180)
from dual
COS(180*3.14159265359/180)

1
Date Arithmetic
When arithmetic operators are used with DATE datatype it is called as Date Arithmetic.
The following are the possible arithmetic operations on DATE type data.
Adding a number to date to get the date after the given number of days.
Subtracting a number from a date to get the date before the given number of days.
Subtracting two dates to get the number of days between these two dates.
The following example displays the name of the student and number of days between system date and date of joining.
select name, sysdate  dj from students;
NAME No Days
 
George Micheal 226.29194
Micheal Douglas 225.29194
Andy Roberts 225.29194
Malcom Marshall 220.29194
Vivan Richards 220.29194
Chirs Evert 222.29194
Ivan Lendal 221.29194
George Micheal 176.29194
Richard Marx 140.29194
Tina Turner 140.29194
Jody Foster 139.29194
In Oracle DATE datatype stores date and time. At the time of storing a date If time is not given then it will be set to 0 hours, 0 minutes and 0 seconds (beginning of the day or 12:00 a.m.).
Default date format – DDMONYY – doesn’t include time. However time is always stored along with date and if you want to at any time you can extract the time portion a date using TO_CHAR function, which will be discussed in the next chapter.
Note: All comparisons between two dates include time portion also.
Note: The fraction portion in the result between two dates indicates the difference in time.
The following example shows the due date for first installment (assuming first installment is to be paid within 10 days from the date of joining).
select name,dj, dj + 10 "Due Date" from students
NAME DJ Due Date
  
George Micheal 10JAN01 20JAN01
Micheal Douglas 11JAN01 21JAN01
Andy Roberts 11JAN01 21JAN01
Malcom Marshall 16JAN01 26JAN01
Vivan Richards 16JAN01 26JAN01
Chirs Evert 14JAN01 24JAN01
Ivan Lendal 15JAN01 25JAN01
George Micheal 01MAR01 11MAR01
Richard Marx 06APR01 16APR01
Tina Turner 06APR01 16APR01
Jody Foster 07APR01 17APR01
The following query displays the details of the payment that were made in the last 3 days:
select * from payments
Where sysdate – dp <= 3;
Date Functions
Date functions operate on values of DATE datatype. Except MONTHS_BETWEEN all date functions return DATE data type. The following is the list of DATE functions.
Function Description
ADD_MONTHS(date, count) Adds count number of months to date.
MONTHS_BETWEEN (date1, date2) Returns number of months between date1 and date2.
LAST_DAY(date) Returns the last day of the month in which date is.
NEXT_DAY(date, ’day’) Gives the date of next day after the date, where day name of the week like ‘Monday’.
NEW_TIME(date, ’this’, ’other’) Returns time in other time zone for time of this time zone.
ROUND(date) Rounds the date depending upon the time. If time is at or after 12 hours then date is incremented. Time is always set to beginning of the day (0:0:0).
TRUNC(date)
Same as ROUND (date) but doesn’t increment date.
Table 3: DATE Functions.
Adding and subtracting months
You can add or subtract months from a date using ADD_MONTHS function. If the count is positive, that many months will be added. If count is negative that many months will be subtracted.
Adding months is the process where Oracle will give the date of next specified number of months.
In the following example, Oracle will add two months to system date:
SQL> Select sysdate, add_months(sysdate,2)
2 From dual;
SYSDATE ADD_MONTH
 
25AUG01 25OCT01
If the target month doesn’t have the required day then the last day of the month will be taken. In the following example, 30SEP2001 is returned, as 31SEP is not available. Oracle automatically adjusts the date according to the requirement.
SQL> select add_months('31aug2001',1) from dual;
ADD_MONTH

30SEP01
The following example will show the date on which the students of completed batches will be issued certificates assuming it will take 3 months time to issue certificates.
SQL> select bcode, ccode, enddate, add_months(enddate,3) "Cert. Date"
2 from batches
3 where enddate is not null;
BCODE CCODE ENDDATE Cert. Dat
   
b1 ora 20FEB01 20MAY01
b2 asp 05MAR01 05JUN01
b3 c 27FEB01 27MAY01
b4 xml 30MAR01 30JUN01
b5 java 10MAY01 10AUG01
When the second parameter – count  is negative, date is decremented by that many months.
The following example shows the date on which the admissions for running batches have started. For a batch admissions start exactly one month before the starting date.
select bcode, ccode, stdate, add_months(stdate,1)
from batches where enddate is null
BCODE CCODE STDATE ADD_MONTH
   
b6 vbnet 12JUL01 12JUN01
b7 ora 15AUG01 15JUL01
Getting months between two dates
You can obtain the number of months between two dates using MONTHS_BETWEEN function. The following query returns the number of months between starting date and ending date of all completed batches.
select bcode, ccode, stdate, enddate,
months_between(enddate, stdate) "NO. Months"
from batches where enddate is not null;
BCODE CCODE STDATE ENDDATE NO. Months
    
b1 ora 12JAN01 20FEB01 1.2580645
b2 asp 15JAN01 05MAR01 1.6774194
b3 c 20JAN01 27FEB01 1.2258065
b4 xml 02MAR01 30MAR01 .90322581
b5 java 05APR01 10MAY01 1.1612903
The fraction in the result is the number of days beyond the number of months. For example, the difference between 12JAN01 and 20FEB01 is 1.258. It means there is one month and 26% of another month, which comes to 8 days.
Note: The fraction is calculated based on a 31day month and also considers time portion.
Use TRUNC function to ignore fraction in the result of MONTHS_BETWEEN as follows:
select bcode, ccode, stdate, enddate,
trunc(months_between( enddate, stdate)) "NO. Months"
from batches where enddate is not null;
BCODE CCODE STDATE ENDDATE NO. Months
    
b1 ora 12JAN01 20FEB01 1
b2 asp 15JAN01 05MAR01 1
b3 c 20JAN01 27FEB01 1
b4 xml 02MAR01 30MAR01 0
b5 java 05APR01 10MAY01 1
Note: It is possible to send the return value of a function to another function.
The following query displays the batches that we completed in the last 6 months and duration is more that 1 month.
select bcode, ccode
from batches
where months_between(sysdate,enddate) <= 6
and months_between(enddate,stdate) > 1;
BCODE CCODE
 
b2 asp
b3 c
b5 java
LAST_DAY function
LAST_DAY function returns the date of the last day of the month of the given date. The following statement displays the last day of the current month:
Select sysdate, last_day(sysdate)
From dual;
SYSDATE LAST_DAY(
 
25AUG01 31AUG01
The following query displays the due date by which first installment of each batch is to be paid. LAST_DAY function return the last day of the month in which batch has started and if 5 is added to that then it will be 5th of the next month – due date of first installment.
select bcode,ccode, stdate, last_day(stdate) + 5 "Due Date"
from batches
BCODE CCODE STDATE Due Date
   
b1 ora 12JAN01 05FEB01
b2 asp 15JAN01 05FEB01
b3 c 20JAN01 05FEB01
b4 xml 02MAR01 05APR01
b5 java 05APR01 05MAY01
b6 vbnet 12JUL01 05AUG01
b7 ora 15AUG01 05SEP01
Similarly assuming the batches are scheduled in the last week of previous month for each batch, the following query displays the date of last week:
select bcode, ccode, stdate, last_day(add_months(stdate,1))  7 
' to '  last_day(add_months(stdate), 1)
from batches
BCODE CCODE STDATE Schd. Week
   
b1 ora 12JAN01 24DEC00 to 31DEC00
b2 asp 15JAN01 24DEC00 to 31DEC00
b3 c 20JAN01 24DEC00 to 31DEC00
b4 xml 02MAR01 21FEB01 to 28FEB01
b5 java 05APR01 24MAR01 to 31MAR01
b6 vbnet 12JUL01 23JUN01 to 30JUN01
b7 ora 15AUG01 24JUL01 to 31JUL01
NEXT_DAY function
This function returns the date of given weekday that is greater than the given date. It takes weekday – Sunday, Monday etc. – and returns the date on which the coming weekday is falling. The return value is always grater than the given date. The following example shows when is the next Friday.
select sysdate, next_day(sysdate,'Fri') from dual;
SYSDATE NEXT_DAY(
 
25AUG01 31AUG01
If weekday of the given date and the given weekday happen to be the same then the date of coming weekday is returned. This is because the result of this function is always greater than the given date. See the following example where though the given date  25AUG  is Saturday NEXT_DAY returns the next Saturday and not the same date.
select sysdate, next_day(sysdate,'Sat') from dual
SYSDATE NEXT_DAY(
 
25AUG01 01SEP01
But what if you want to get the same date, when day of the week of the given date is same as the one asked for? The following query will return the same date if date happens to fall on the required weekday.
select sysdate, next_day(sysdate  1,'Sat') from dual
SYSDATE NEXT_DAY(
 
25AUG01 25AUG01
When one is subtracted from the system date, though the date happens to be on Saturday it become Friday (24AUG) because of the subtraction. Then NEXT_DAY returns the 25AUG as it is grater than the given date – 24AUG.
ROUND & TRUNC functions with dates
DATE data type contains both date and time. ROUND and TRUNC function can be used to round or truncate the date based on the time portion. The following query displays the date and time portion of system date using TO_CHAR function. It is suffice to know that TO_CHAR can be used to convert given date to character type using the given format.
Select to_char(sysdate,'ddmmyyyy hh24:mi:ss') from dual
TO_CHAR(SYSDATE,'DD

25082001 18:42:08
Note: TO_CHAR converts a DATE type data to character type. Please see next chapter for more information on TO_CHAR.
ROUND function adds one day to the date if time portion of the date is greater than or equal to 12 noon.
select sysdate, to_char(round(sysdate),'ddmmyyyy hh24:mi:ss') “Round Date" from dual
SYSDATE Round Date
 
25AUG01 26082001 00:00:00
In the above query first ROUND function is used to round SYSDATE. As we have seen the time in SYSDATE is 18 hours, the date is incremented by one – 26AUG. ROUND always sets the time portion to 0:0:0 (as seen in the output of the query).
TRUNC function doesn’t increment the date based on the time, but it sets time portion to 0 hours, 0 minutes and 0 seconds. The following query shows the result of TRUNC function.
select to_char(sysdate,'ddmmyyyy hh24:mi:ss') "Today",
to_char( trunc(sysdate),'ddmmyyyy hh24:mi:ss') "Truncated Date"
from dual
Today Truncated Date
 
25082001 18:56:53 25082001 00:00:00
Note: Both ROUND and TRUNC set the time portion in the DATE data type to 12 A.M. (00:00:00).
The following query is used to displays the details of the payments made today.
select * from payments
where dp = sysdate;
The above query always returns no rows selected. This is because when Oracle compares two dates it takes date and time portions into account. In the above query, though PAYMENTS table contains rows where DP is containing the same date as SYSDATE, the time portions will not match. The remedy is to ignore time portions and compare only date portions of the dates. The following is revised query where we truncate the dates to set both the times to 0:0:0 so that only dates are compared as times are equal.
select * from payments
where trunc(dp) = trunc(sysdate);
The following is another example where TRUNC is used to ignore time portion of DP and compare date with 10apr2001.
select * from payments
where trunc(dp) = '10apr2001'
ROLLNO DP AMOUNT
  
10 10APR01 4500
11 10APR01 3500
Getting time in different time zone
NEW_TIME is used to return the time of the specified time zone for the time of the given time zone.
The following query displays what will be the time in PST for the time in GMT.
select to_char(sysdate,'ddmmyyyy hh24:mi:ss') GMT ,
to_char( new_time(sysdate,'GMT','AST'),'ddmmyyyy hh24:mi:ss') AST
from dual
TO_CHAR(SYSDATE,'DD TO_CHAR(NEW_TIME(SY
 
25082001 19:35:36 25082001 15:35:36
The following are a few of the available time zones. For complete lit, please see Oracle online documentation.
Time Zone Meaning
EST , EDT Eastern Standard or Daylight Time
GMT Greenwich Mean Time
HST , HDT AlaskaHawaii Standard Time or Daylight Time.
PST , PDT Pacific Standard or Daylight Time
AST , ADT Atlantic Standard or Daylight Time
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