SpirirHost Support Centre: MySQL Reference Manual p.401

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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

Chapter 6: MySQL Language Reference 401 means that column values are sorted and compared in case-sensitive fashion according to the ASCII order of the machine where the MySQL server is running. BINARY doesn't aect how the column is stored or retrieved. The BINARY attribute is sticky. This means that if a column marked BINARY is used in an expression, the whole expression is compared as a BINARY value. MySQL may silently change the type of a CHAR or VARCHAR column at table creation time. See Section 6.5.3.1 [Silent column changes], page 476. 6.2.3.2 The BLOB and TEXT Types A BLOB is a binary large object that can hold a variable amount of data. The four BLOB types TINYBLOB, BLOB, MEDIUMBLOB, and LONGBLOB dier only in the maximum length of the values they can hold. See Section 6.2.6 [Storage requirements], page 405. The four TEXT types TINYTEXT, TEXT, MEDIUMTEXT, and LONGTEXT correspond to the four BLOB types and have the same maximum lengths and storage requirements. The only dierence between BLOB and TEXT types is that sorting and comparison is performed in case-sensitive fashion for BLOB values and case-insensitive fashion for TEXT values. In other words, a TEXT is a case-insensitive BLOB. If you assign a value to a BLOB or TEXT column that exceeds the column type's maximum length, the value is truncated to t. In most respects, you can regard a TEXT column as a VARCHAR column that can be as big as you like. Similarly, you can regard a BLOB column as a VARCHAR BINARY column. The dierences are: You can have indexes on BLOB and TEXT columns with MySQL Version 3.23.2 and newer. Older versions of MySQL did not support this. There is no trailing-space removal for BLOB and TEXT columns when values are stored, as there is for VARCHAR columns. BLOB and TEXT columns cannot have DEFAULT values. MyODBC denes BLOB values as LONGVARBINARY and TEXT values as LONGVARCHAR. Because BLOB and TEXT values may be extremely long, you may run up against some con- straints when using them: If you want to use GROUP BY or ORDER BY on a BLOB or TEXT column, you must convert the column value into a xed-length object. The standard way to do this is with the SUBSTRING function. For example: mysql> SELECT comment FROM tbl_name,SUBSTRING(comment,20) AS substr -> ORDER BY substr; If you don't do this, only the rst max_sort_length bytes of the column are used when sorting. The default value of max_sort_length is 1024; this value can be changed using the -O option when starting the mysqld server. You can group on an expression involving BLOB or TEXT values by specifying the column position or by using an alias: mysql> SELECT id,SUBSTRING(blob_col,1,100) FROM tbl_name GROUP BY 2; mysql> SELECT id,SUBSTRING(blob_col,1,100) AS b FROM tbl_name GROUP

MySQL Reference Manual

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