To use the name as a function call in an expression, there must be no whitespace between the name and the following ( parenthesis character.要将名称用作表达式中的函数调用，名称和后面跟着的(括号字符之间不能有空格。

Conversely, to use the function name as an identifier, it must not be followed immediately by a parenthesis.相反，要将函数名用作标识符，它后面不能紧跟括号。

ADDDATE

BIT_AND

BIT_OR

BIT_XOR

CAST

COUNT

CURDATE

CURTIME

DATE_ADD

DATE_SUB

EXTRACT

GROUP_CONCAT

MAX

MID

MIN

NOW

POSITION

SESSION_USER

STD

STDDEV

STDDEV_POP

STDDEV_SAMP

SUBDATE

SUBSTR

SUBSTRING

SUM

SYSDATE

SYSTEM_USER

TRIM

VARIANCE

VAR_POP

VAR_SAMP

With IGNORE_SPACE disabled, the parser interprets the name as a function call when there is no whitespace between the name and the following parenthesis. This occurs even when the function name is used in nonexpression context:在IGNORE_SPACE被禁用的情况下，当名称和下面的括号之间没有空格时，解析器将名称解释为函数调用。即使在非压缩上下文中使用函数名，也会出现这种情况：

mysql> CREATE TABLE count(i INT);
ERROR 1064 (42000): You have an error in your SQL syntax ...
near 'count(i INT)'

To eliminate the error and cause the name to be treated as an identifier, either use whitespace following the name or write it as a quoted identifier (or both):为了消除错误并使名称被视为标识符，可以在名称后面使用空格，也可以将其写成带引号的标识符（或两者兼有）：

CREATE TABLE count (i INT);
CREATE TABLE `count`(i INT);
CREATE TABLE `count` (i INT);

With IGNORE_SPACE enabled, the parser loosens the requirement that there be no whitespace between the function name and the following parenthesis. 在启用IGNORE_SPACE的情况下，解析器取消了函数名和下面的括号之间不能有空格的要求。This provides more flexibility in writing function calls. For example, either of the following function calls are legal:这在编写函数调用时提供了更大的灵活性。例如，以下任一函数调用都是合法的：

SELECT COUNT(*) FROM mytable;
SELECT COUNT (*) FROM mytable;

However, enabling IGNORE_SPACE also has the side effect that the parser treats the affected function names as reserved words (see Section 9.3, “Keywords and Reserved Words”). This means that a space following the name no longer signifies its use as an identifier. The name can be used in function calls with or without following whitespace, but causes a syntax error in nonexpression context unless it is quoted. 然而，启用IGNORE_SPACE也有副作用，即解析器将受影响的函数名视为保留字（请参阅第9.3节，“关键字和保留字”）。这意味着名称后面的空格不再表示其用作标识符。该名称可以在带有或不带有空格的函数调用中使用，但在非压缩上下文中会导致语法错误，除非它被引用。For example, with IGNORE_SPACE enabled, both of the following statements fail with a syntax error because the parser interprets count as a reserved word:例如，在启用IGNORE_SPACE的情况下，以下两个语句都会因语法错误而失败，因为解析器将count解释为保留字：

CREATE TABLE count(i INT);
CREATE TABLE count (i INT);

To use the function name in nonexpression context, write it as a quoted identifier:要在非压缩上下文中使用函数名，请将其写成带引号的标识符：

CREATE TABLE `count`(i INT);
CREATE TABLE `count` (i INT);

Avoid creating loadable functions or stored functions that have the same name as a built-in function.避免创建与内置函数同名的可加载函数或存储函数。

Avoid using function names in nonexpression context. For example, these statements use count (one of the affected function names affected by IGNORE_SPACE), so they fail with or without whitespace following the name if IGNORE_SPACE is enabled:避免在非压缩上下文中使用函数名。例如，这些语句使用count（受IGNORE_SPACE影响的受影响函数名之一），因此如果启用IGNORE_SPACE，则在名称后面有空格或没有空格的情况下都会失败：

CREATE TABLE count(i INT);
CREATE TABLE count (i INT);

If you must use a function name in nonexpression context, write it as a quoted identifier:如果必须在非压缩上下文中使用函数名，请将其写成带引号的标识符：

CREATE TABLE `count`(i INT);
CREATE TABLE `count` (i INT);

Built-in functions and loadable functions内置功能和可加载功能

An error occurs if you try to create a loadable function with the same name as a built-in function.如果试图创建与内置函数同名的可加载函数，则会发生错误。

Built-in functions and stored functions内置功能和存储功能

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 schema name. 可以创建与内置函数同名的存储函数，但要调用存储函数，必须使用模式名称对其进行限定。For example, if you create a stored function named PI in the test schema, invoke it as test.PI() because the server resolves PI() without a qualifier as a reference to the built-in function. The server generates a warning if the stored function name collides with a built-in function name. 例如，如果您在测试模式中创建了一个名为PI的存储函数，请将其调用为test.PI()，因为服务器解析PI()时不使用限定符作为对内置函数的引用。如果存储的函数名称与内置函数名称冲突，服务器将生成警告。The warning can be displayed with SHOW WARNINGS.警告可以显示为SHOW WARNINGS。

Loadable functions and stored functions可加载函数和存储函数

Loadable functions and stored functions share the same namespace, so you cannot create a loadable function and a stored function with the same name.可加载函数和存储函数共享相同的命名空间，因此不能创建具有相同名称的可加载函数与存储函数。

If you have already created a loadable function with a given name and upgrade MySQL to a version that implements a new built-in function with the same name, the loadable function becomes inaccessible. 如果您已经创建了一个具有给定名称的可加载函数，并将MySQL升级到实现具有相同名称的新内置函数的版本，则可加载函数将无法访问。To correct this, use DROP FUNCTION to drop the loadable function and CREATE FUNCTION to re-create the loadable function with a different nonconflicting name. Then modify any affected code to use the new name.要更正此问题，请使用DROP FUNCTION删除可加载函数，并使用CREATE FUNCTION使用不同的非冲突名称重新创建可加载函数。然后修改任何受影响的代码以使用新名称。

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). 如果新版本的MySQL实现了与现有存储函数同名的内置函数，则有两种选择：重命名存储函数以使用不冲突的名称，或者更改对该函数的调用以使用架构限定符（即，使用schema_name.func_name()语法）。In either case, modify any affected code accordingly.无论哪种情况，都要相应地修改任何受影响的代码。