1. Lecture 5
SQL FUNCTIONS

2. Functions are a very powerful feature of SQL
Functions are a very powerful feature of SQL. They can be used to do the following:
Perform calculations on data
Modify individual data items
Manipulate output for groups of rows
Format dates and numbers for display
Convert column data types SQL functions sometimes take arguments and always return a value.

3. Types of SQL functions There are two types of functions:
Single-row functions
Multiple-row functions

4. Single Row Functions
These functions operate on single rows only and return one result per row.
There are different types of single-row functions.
Character
Number
Date
Conversion
General

5. Multiple-Row Functions
Functions can manipulate groups of rows to give one result per group of rows. These functions are also known as group functions.
Example:
Avg(),count(),max(),min(),sum()

6. Single Row Function Description
Manipulate data items
Accept arguments and return one value
Act on each row that is returned
Return one result per row
May modify the data type

7. Type of Argument in the Function
User-supplied constant
Variable value
Column name
Expression.
Single row functions can be used in SELECT,WHERE,ORDERBY clauses.

8. Function_name(arg1,arg2…)
Syntax
function_name is the name of the function, arg1, arg2 is any argument to be used by the function.
This can be represented by a column name or expression.
Function_name(arg1,arg2…)

9. Type of Single Row Functions
 Character functions: Αccept character input and can return both character and number values
Number functions: Accept numeric input and return numeric values
Date functions: Operate on values of the DATE data type.
Conversion functions: Convert a value from one data type to another
General functions: - NVL,NVL2,NULLIF,CASE,DECODE

10. Character Function
Two types: Case conversion function. Character manipulation functions.

11. Case Conversion Function
LOWER, UPPER
LOWER
Converts alpha character values to lowercase
SELECT LOWER(ENAME)
FROM employee

12. UPPER:
Converts alpha character values to uppercase.
SELECT UPPER(ENAME)
FROM employee

13. Character Manipulation Function
CONCAT,SUBSTR.LENGTH,TRIM
CONCAT:
Joins values together (You are limited to using two parameters with CONCAT.)
SELECT CONCAT(ENAME,EMPLNO)
FROM employee
• SUBSTR:
Extracts a string of determined length
SELECT SUBSTR(ENAME,1,5)

14. LENGTH:
Shows the length of a string as a numeric value
SELECT length(ENAME)
FROM employee
• INSTR:
Finds numeric position of a named character
SELECT INSTR(ENAME,'A')

15. Replace
Replace lets you substitute one string for another as well as to remove character strings.
Select replace(‘JACK’, ‘J’, ‘BL’);
Output: BLACK
Reverse:
Reverse characters in a string
Select reverse(‘abcd’);
Output: dcba

16. MID()
Used to extract character from the text field.
MID(name, 1 ,4)

17. Number Function ROUND: Rounds value to a specified decimal
Result:
TRUNC: Truncates value to a specified decimal
TRUNCATE(45.436,2)
Result:
MOD: Returns remainder of division
MOD(1600,300)
Result: 100

18. Controlling for number precision
Ceil and floor functions are used to round either up or down to the closest integer.
Select ceil(72.445) 73
floor(72.445) 72

19. DATE FUNCTIONS
Used to perform date calculations or format date values.
MYSQL displays date in this format'YYYY-MM-DD' 
Curdate() for retrieving current date.
CURTIME() for retrieving current time
NOW() for retrieving time and date.