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Reserved Words

758

It is possible to create a stored function with the same name as a built-in function, but to invoke the
stored function it is necessary to qualify it with a database name. For example, if you create a stored
function named

in the

test

database, you invoke it as

test.PI()

because the server resolves

PI()

[911]

as a reference to the built-in function.

• User-defined functions and stored functions

User-defined functions and stored functions share the same namespace, so you cannot create a
UDF and a stored function with the same name.

The preceding function name resolution rules have implications for upgrading to versions of MySQL
that implement new built-in functions:

• If you have already created a user-defined function with a given name and upgrade MySQL to a

version that implements a new built-in function with the same name, the UDF becomes inaccessible.
To correct this, use

DROP FUNCTION

to drop the UDF, and then use

CREATE FUNCTION

to re-

create the UDF with a different nonconflicting name.

• If a new version of MySQL implements a built-in function with the same name as an existing stored

function, you have two choices: Rename the stored function to use a nonconflicting name, or change
calls to the function so that they use a schema qualifier (that is, use

schema_name.func_name()

syntax).

9.3. Reserved Words

Certain words such as

SELECT

DELETE

, or

BIGINT

are reserved and require special treatment for

use as identifiers such as table and column names. This may also be true for the names of built-in
functions.

Reserved words are permitted as identifiers if you quote them as described in

Section 9.2, “Schema

Object Names”

mysql>

CREATE TABLE interval (begin INT, end INT);

ERROR 1064 (42000): You have an error in your SQL syntax ...

near 'interval (begin INT, end INT)'

mysql>

CREATE TABLE `interval` (begin INT, end INT);

Query OK, 0 rows affected (0.01 sec)

Exception: A word that follows a period in a qualified name must be an identifier, so it need not be
quoted even if it is reserved:

mysql>

CREATE TABLE mydb.interval (begin INT, end INT);

Query OK, 0 rows affected (0.01 sec)

Names of built-in functions are permitted as identifiers but may require care to be used as such. For
example,

COUNT

is acceptable as a column name. However, by default, no whitespace is permitted

in function invocations between the function name and the following “

(

” character. This requirement

enables the parser to distinguish whether the name is used in a function call or in nonfunction context.
For further detail on recognition of function names, see

Section 9.2.3, “Function Name Parsing and

Resolution”

The words in the following table are explicitly reserved in MySQL 5.0. At some point, you might
upgrade to a higher version, so it is a good idea to have a look at future reserved words, too. You
can find these in the manuals that cover higher versions of MySQL. Most of the words in the table
are forbidden by standard SQL as column or table names (for example,

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