Lecture 5 SQL FUNCTIONS

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.

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

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

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()

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

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.

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…)

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

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

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

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

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)

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')

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

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

Number Function ROUND: Rounds value to a specified decimal Result: 45.44 TRUNC: Truncates value to a specified decimal TRUNCATE(45.436,2) Result: 45.43 MOD: Returns remainder of division MOD(1600,300) Result: 100

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

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.