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    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 379 NULL  may be represented by  \N  when using the text le import or export formats (LOAD DATA INFILE, SELECT ... INTO OUTFILE).  See Section 6.4.9 [LOAD DATA], page 461. 6.1.2  Database, Table, Index, Column, and Alias Names Database, table, index, column, and alias names all follow the same rules in MySQL. Note that the rules changed starting with MySQL Version 3.23.6 when we introduced quot- ing of identi ers (database, table, and column names) with ``'.  `"' will also work to quote identi ers if you run in ANSI mode.  See Section 1.7.2 [ANSI mode], page 31. Identi er Max length Allowed characters Database 64 Any character that is allowed in a directory name except `/', `\' or `.'. Table 64 Any character that is allowed in a le name, except `/' or `.'. Column 64 All characters. Alias 255 All characters. Note that in addition to the above, you can't have ASCII(0) or ASCII(255) or the quoting character in an identi er. Note that if the identi er is a restricted word or contains special characters you must always quote it with ` when you use it: mysql> SELECT * FROM `select` WHERE `select`.id > 100; See Section 6.1.7 [Reserved words], page 385. In MySQL versions prior to 3.23.6, the name rules are as follows:    A name may consist of alphanumeric characters from the current character set and also `_' and `$'.  The default character set is ISO-8859-1 Latin1; this may be changed with the --default-character-set option to mysqld.  See Section 4.6.1 [Character sets], page 267.    A name may start with any character that is legal in a name.  In particular, a name may start with a digit (this di ers from many other database systems!).  However, a name cannot consist only  of digits.    You cannot use the `.' character in names because it is used to extend the format by which you can refer to columns (see immediately below). It is recommended that you do not use names like 1e, because an expression like 1e+1 is ambiguous.  It may be interpreted as the expression 1e + 1 or as the number 1e+1. In MySQL you can refer to a column using any of the following forms: Column reference Meaning col_name Column  col_name  from  whichever  table  used  in  the  query contains a column of that name. tbl_name.col_name Column   col_name   from   table   tbl_name   of   the   current database. db_name.tbl_name.col_ name Column col_name from table tbl_name of the database db_ name.  This form is available in MySQL Version 3.22 or later.
     

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