Functions

You can use expressions with functions. These functions can be applied to the data in the results table or specified in search conditions.

Prerequisites

You can use the demo data for the SQL tutorial. Start the Database Studio as database administrator MONA with the password RED and log on to demo database DEMODB: Logging On to a Database.

Activities

Function Descriptions in the Reference Manual	Examples of this Function Group
Arithmetic Function (arithmetic_function)	`TRUNC`, `SIGN`, `ABS`
Trigonometric Function (trigonometric_function)	`SIN`, `ATAN`, `DEGREES`
String Function (string_function)	`SUBSTR`, `UPPER`, `MAPCHAR`
Date Function (date_function)	`SUBDATE`, `DAYOFMONTH`, `DAYNAME`
Time Function (time_function)	`ADDTIME`, `TIMEDIFF`, `MAKETIME`
Extraction (extraction_function)	`DAY`, `TIMESTAMP`, `DATE`
Special Function (special_function)	`VALUE`, `LEAST`, `CASE` functions
Conversion Function (conversion_function)	`NUM`, `HEXTOROW`, `CHAR`
Database Function Call (dbfunction_call)	Call of a database function defined using `CREATE FUNCTION`

See also: SQL Reference Manual, Function (dbfunction_call)

Most of these functions are self-explanatory. For this reason, examples of just a few selected functions will be given here.

You can use Database Studio to enter and execute SQL statements. More information: Working with SQL Statements: Overview

String Functions

You can use the string functions to change the display of character strings.

SELECT cno, name & ', ' & firstname name

FROM hotel.customer

WHERE cno = 3000

First and last names are linked to one another.

Result

`CNO`	`NAME`
`3000`	`Porter, Jenny`

See also: SQL Reference Manual, Concatenation (concatenation)

SELECT cno, SUBSTR(firstname,1,1) & '. ' & name name

FROM hotel.customer

WHERE cno = 3000

First and last names are linked to one another; the first name is displayed in initials only.

Result

`CNO`	`NAME`
`3000`	`J. Porter`

See also: SQL Reference Manual, SUBSTR(x,a,b)

Date Functions

Date functions are applied to date and timestamp values or return a date or timestamp value as a result.

SELECT rno, arrival, DAYNAME(arrival) arrival_day

FROM hotel.reservation

WHERE rno < 150

Displaying the day of arrival

Result

`RNO`	`ARRIVAL`	`ARRIVAL_DAY`
`100`	`2004-11-13`	`Saturday`
`110`	`2004-12-24`	`Friday`
`120`	`2004-11-14`	`Sunday`
`130`	`2005-02-01`	`Tuesday`
`140`	`2004-04-12`	`Monday`

See also: SQL Reference Manual, DAYNAME/MONTHNAME(t)

Extractions

You can use extraction functions to display parts of date, time, or timestamp values or to create date, time, or timestamp values.

SELECT name, 675456 number_of_days, DATE(675456) counted_date

FROM hotel.city

WHERE zip = '12203'

Displaying when 675456 days after 31.12.0000 have passed

Result

`NAME`	`NUMBER_OF_DAYS`	`COUNTED_DATE`
`Albany`	`675456`	`1850-05-03`

See also: SQL Reference Manual, DATE(a)

General CASE Function

The general CASE function analyzes a sequence of search conditions and delivers a result for each search condition.

SELECT hno,

CASE

WHEN price IS NULL THEN 'Not yet priced'

WHEN price < 70 THEN 'Very cheap'

WHEN price >= 70 AND price < 100 THEN 'Normal price'

ELSE 'Expensive hotel'

END price_range

FROM hotel.room

WHERE hno < 100 AND type = 'single'

Estimating the price classes of single rooms in a selection of hotels

Result

`HNO`	`PRICE_RANGE`
`10`	`Expensive hotel`
`20`	`Normal price`
`30`	`Very cheap`
`40`	`Normal price`
`50`	`Expensive hotel`
`60`	`Expensive hotel`
`70`	`Expensive hotel`
`80`	`Normal price`
`90`	`Normal price`

See also: SQL Reference Manual, General CASE Function (searched_case_function)

Simple CASE Function

The simple CASE function compares an expression with a sequence of simple expressions to determine in each case a result expression.

SELECT hno,

CASE price

WHEN NULL THEN 'Not yet priced'

WHEN 70 THEN 'Very cheap'

WHEN 90 THEN 'Cheap'

WHEN 100 THEN 'Normal hotel'

WHEN 115 THEN 'Expensive hotel'

WHEN 135 THEN 'Very expensive hotel'

ELSE 'Not yet in price_range list'

END price_range

FROM hotel.room

WHERE hno < 100 AND type = 'single'

Comparing the prices of a selection of hotels with a rating scale for single room prices

Result

`HNO`	`PRICE_RANGE`
`10`	`Very expensive hotel`
`20`	`Very cheap`
`30`	`Not yet in price_range list`
`40`	`Not yet in price_range list`
`50`	`Not yet in price_range list`
`60`	`Not yet in price_range list`
`70`	`Expensive hotel`
`80`	`Cheap`
`90`	`Cheap`

See also: SQL Reference Manual, Simple CASE Function (simple_case_function)

Database function

Before you can execute this example, you have to create the database function avgprice(zip), as described in Database Functions.

SELECT hno, avgprice(zip) avgprice

FROM hotel.hotel

WHERE hno = 40

Result

`HNO`	`AVGPRICE`
`40`	`87.5`

See also: SQL Reference Manual, Database Function Call (dbfunction_call)

More Information

More examples for Data Query