SpirirHost Support Centre: MySQL Reference Manual p.406

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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

406 MySQL Technical Reference for Version 4.0.3 Storage requirements for string types Column type Storage required CHAR(M) M bytes, 1 <= M <= 255 VARCHAR(M) L+1 bytes, where L <= M and 1 <= M <= 255 TINYBLOB, TINYTEXT L+1 bytes, where L < 2^8 BLOB, TEXT L+2 bytes, where L < 2^16 MEDIUMBLOB, MEDIUMTEXT L+3 bytes, where L < 2^24 LONGBLOB, LONGTEXT L+4 bytes, where L < 2^32 ENUM('value1','value2',...) 1 or 2 bytes, depending on the number of enumeration values (65535 values maximum) SET('value1','value2',...) 1, 2, 3, 4 or 8 bytes, depending on the number of set members (64 members maximum) VARCHAR and the BLOB and TEXT types are variable-length types, for which the storage re- quirements depend on the actual length of column values (represented by L in the preceding table), rather than on the type's maximum possible size. For example, a VARCHAR(10) col- umn can hold a string with a maximum length of 10 characters. The actual storage required is the length of the string (L), plus 1 byte to record the length of the string. For the string 'abcd', L is 4 and the storage requirement is 5 bytes. The BLOB and TEXT types require 1, 2, 3, or 4 bytes to record the length of the column value, depending on the maximum possible length of the type. See Section 6.2.3.2 [BLOB], page 401. If a table includes any variable-length column types, the record format will also be variable- length. Note that when a table is created, MySQL may, under certain conditions, change a column from a variable-length type to a xed-length type, or vice-versa. See Section 6.5.3.1 [Silent column changes], page 476. The size of an ENUM object is determined by the number of dierent enumeration values. One byte is used for enumerations with up to 255 possible values. Two bytes are used for enumerations with up to 65535 values. See Section 6.2.3.3 [ENUM], page 402. The size of a SET object is determined by the number of dierent set members. If the set size is N, the object occupies (N+7)/8 bytes, rounded up to 1, 2, 3, 4, or 8 bytes. A SET can have a maximum of 64 members. See Section 6.2.3.4 [SET], page 403. 6.3 Functions for Use in SELECT and WHERE Clauses A select_expression or where_definition in a SQL statement can consist of any ex- pression using the functions described below. An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for the operators and functions involved in the expression. Note: there must be no whitespace between a function name and the parentheses following it. This helps the MySQL parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. Spaces around arguments are permitted, though.

MySQL Reference Manual

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