pengertian Identifiers
You can reference any given object on a MySQL server—assuming
you have the proper rights—using one of the following conventions:
- Absolute naming
- Relative naming
-
Relative naming allows you to specify only part of the object's name, with the rest of the name being assumed based on your current context. For example, if you are currently connected to the BANK database, you can reference the BANK.ACCOUNT.BALANCE column as ACCOUNT.BALANCE. In an SQL query where you have specified that you are selecting from the ACCOUNT table, you may reference the column using only BALANCE. You must provide an extra layer of context whenever relative naming might result in ambiguity. An example of such ambiguity would be a SELECT statement pulling from two tables that both have BALANCE columns.
- Aliasing
-
Aliasing enables you to reference an object using an alternate name that helps avoid both ambiguity and the need to fully qualify a long name.
In general, MySQL allows you to use any character in an
identifier. (Older versions of MySQL limited identifiers to valid alphanumeric
characters from the default character set, as well as $ and
_.) This rule is limited, however, for databases and tables, because
these values must be treated as files on the local filesystem. You can therefore
use only characters valid for the underlying filesystem's naming conventions in
a database or table name. Specifically, you may not use / or . in a database or
table name. You can never use NUL (ASCII 0) or ASCII 255 in an identifier.
When an identifier is also an SQL keyword, you must enclose the
identifier in backticks:
CREATE TABLE 'select' ( 'table' INT NOT NULL PRIMARY KEY AUTO_INCREMENT);
Since Version 3.23.6, MySQL supports the quoting of identifiers
using both backticks and double quotes. For ANSI compatibility, however, you
should use double quotes for quoting identifiers. You must, however, be running
MySQL in ANSI mode.
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