SpirirHost Support Centre: MySQL Reference Manual p.438

<< previous page -- table of contents -- next page >>

Chapter_1

Chapter_2

Chapter_3

Chapter_4

Chapter_5

Return to Table of Contents

Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

438 MySQL Technical Reference for Version 4.0.3 To cast a string to a numeric value, you don't normally have to do anything; just use the string value as it would be a number: mysql> SELECT 1+'1'; -> 2 MySQL supports arithmetic with both signed and unsigned 64-bit values. If you are using an numerical operations (like +) and one of the operands are unsigned integer, then the result will be unsigned. You can override this by using the SIGNED and UNSIGNED cast operators, which will cast the operation to a signed or unsigned 64-bit integer, respectively. mysql> SELECT CAST(1-2 AS UNSIGNED) -> 18446744073709551615 mysql> SELECT CAST(CAST(1-2 AS UNSIGNED) AS SIGNED); -> -1 Note that if either operation is a oating-point value (In this context DECIMAL() is regarded as a oating-point value) the result will be a oating-point value and is not aected by the above rule. mysql> SELECT CAST(1 AS UNSIGNED) -2.0 -> -1.0 If you are using a string in an arithmetic operation, this is converted to a oating-point number. The CAST() and CONVERT() functions were added in MySQL 4.0.2. The handing of unsigned values was changed in MySQL 4.0 to be able to support BIGINT values properly. If you have some code that you want to run in both MySQL 4.0 and 3.23 (in which case you probably can't use the CAST function), you can use the following trick to get a signed result when subtracting two unsigned integer columns: SELECT (unsigned_column_1+0.0)-(unsigned_column_2+0.0); The idea is that the columns are converted to oating-point before doing the subtraction. If you get a problem with UNSIGNED columns in your old MySQL application when porting to MySQL 4.0, you can use the --sql-mode=NO_UNSIGNED_SUBTRACTION option when starting mysqld. Note however that as long as you use this, you will not be able to make ecient use of the UNSIGNED BIGINT column type. 6.3.6 Other Functions 6.3.6.1 Bit Functions MySQL uses BIGINT (64-bit) arithmetic for bit operations, so these operators have a max- imum range of 64 bits. | Bitwise OR mysql> SELECT 29 | 15; -> 31 The result is an unsigned 64-bit integer.

MySQL Reference Manual

Home
Hosting Plans \| Domain Registration \| About Us \| Contact Us \| Site Map Terms of Use \| Privacy Policy \| Guarantees Merchant Accounts

SpiritHost - web hosting for spiritual and education sites SpiritHit.com - Religious and Spiritual Portal Copyright © 2002 Dyntex Group, Inc. All Rights Reserved

Return to Table of Contents	Back to top

Web Hosting: Manuals & FAQ's

1. Unix-Based Web Hosting
2. Unix Dedicated Servers
3. Windows Dedicated Servers
4. CuteFTP User’s Guide
5. CuteHTML User’s Guide
6. WS_FTP Pro User's Guide
7. Miva Order User's Guide
8. Miva Merchant User's Guide