Functions

Functions

Oracle Labs 5 & 6

2/3/2005 Adapted from Introduction to Oracle: SQL and PL/SQL

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SQL Functions

Function

arg n

arg 2

arg 1

.

.

.

Input

ResultingValue

Output


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SQL Functions

• Single-Row Functions• Multiple-Row Functions


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Single-Row Functions

• Acts on each row• Can accept multiple arguments

– Column name– Variable name– Expression– Constant

• Returns a single value for each row


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Single-Row Function Use

• Select• Where• Order By• Any where a column name can be used


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Single-Row Function Types

• Character• Number• Date• Conversion• General


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Character Functions

• LOWER• UPPER• INITCAP

• CONCAT• SUBSTR• LENGTH• INSTR• LPAD• RPAD• TRIM• REPLACE

Case conversion functions

Character manipulation functions

Characterfunctions


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Character FunctionsFunction Purpose

LOWER(column\expression) Converts alpha character values to lowercase

UPPER(column\expression) Converts alpha character values to uppercase

INITCAP(column\expression) Converts alpha character values to uppercase for the first letterOf each word, all other letters in lowercase

CONCAT(column\expression\expression1,Column2\expression2)

Concatenates the first character value to the second character value; equivalent to concatenation operator(||)

SUBSTR(column\expressio,m[,n]) Returns specified characters from character value starting atCharacter position m, n characters long (If m is negative, the count starts

from the end of the character value. If n is omitted, all characters to the end of the string are returned.)

LENGTH(column\expression) Returns the number of characters in value

INSTR(column\expression, m) Returns the numeric position of a named character

LPAD(column\expression, n, ‘string’)

Pads the character value right-justified to a total width of N character positions

TRIM(leading\trailing\both,trim_character FROMtrim_source)

Enables you to trim heading or trailing characters (or both) fromA character string. If trim_character or trim_source is a character literal, you

must enclose it in single quotes.


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Character Functions Oracle Examples

• Accepts character Input• Returns a single value• Value can be

– Character– Numeric

Function_name (column|expression, [arg1, arg2,…])


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Other Single Row Functions

• Number functions• Date functions• Format functions• Conversion functions


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NVL FunctionConverts Null to a Value

• Syntax NVL (expr1, expr2)• expr1

– Source value or expression – that may contain null

• expr2 value to replace null


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NVL Function

• Datatypes could be– Date – Character– Number

• Datatypes must match.– NVL(comm, 0)– NVL(hiredate, ’01-Jan-97’)– NVL(job, ‘No Job Yet’)


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Good Things to Know

• Whole number too large– For format model– Replaced by string of pound signs (#)

• Decimal value too large– For format model– Replaced by rounded value

Multiple-Row Functions

Or Group Functions


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Multiple Rows Single Result

ENAME SAL

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

SMITH 800

ALLEN 1600

WARD 1250

JONES 2975

MARTIN 1250

BLAKE 2850

CLARK 2450

SCOTT 3000

KING 5000

TURNER 1500

ADAMS 1100

JAMES 950

FORD 3000

MILLER 1300

MAX(SAL)

----------

5000


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Types of Group Functions

• AVG• COUNT• MAX• MIN• STDDEV• SUM• VARIANCE


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SELECT [column,] groupfunction(column)FROM table[WHERE condition][GROUP BY group_by_expression][HAVING group_condition][ORDER BY column]


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Functions for Only Numeric Data

• AVG• SUM• VARIANCE• STDDEV

• MAX & MIN used for any datatype


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Examples


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The Count Function

• COUNT(*) – Number of rows in the table – Including

• Duplicate rows• Null Values

• Example


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The Count Function

• COUNT(expr) – Number of nonnull rows in

• The column• Identified by expr

• Example


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Group Functions & Null Values

• Null values ignored in calculations• Use NVL function to ‘work-around’• Examples


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Function Description

AVG(|DISTINCT|ALL|n) Average value of n, ignoring null values

COUNT({*|DISTINCT|ALL|expr}) Number of rows, where expr evaluates to something other than null. (* counts duplicates and nulls)

MAX(|DISTINCT|ALL|expr) Maximum value ignoring null values

MIN(|DISTINCT|ALL|expr) Minimum value ignoring null values

STDDEV(|DISTINCT|ALL|n) Standard deviation of n, ignoring null values

Sum(|DISTINCT|ALL|n) Sum of n, ignoring null values

VARIANCE(|DISTINCT|ALL|n) Variance of n, ignoring null values


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DISTINCT Option

• Consideration of only non-duplicate values• Default – ALL• Example


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Groups Within Groups

• Multiple columns in Group By clause• Top-level group listed first• Example


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ProblemDisplay the deptno and average salary

of all departments that have an average salary greater than 2000.


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HAVING Clause

• Restricts – groups of rows– Based on group conditions

• Like Where clause– Filters– Based on single-row conditions

• After GROUP BY• Before ORDER BY


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Having Clause Oracle Server Steps

1. Group rows.2. Apply group function.3. Filter

• by matching criteria • in HAVING clause

EXAMPLE PROBLEM

Functions

Documents

plsqlsinglerow functionsacts

number of rows

decimal value

rounded value

nullexpr2 value

single valuevalue

expressionhaving group

expr2expr1 source value