ASCII(str)

Returns the numeric value of the leftmost character of the string str. 返回字符串str最左边的字符的数值。Returns 0 if str is the empty string. 如果str是空字符串，则返回0。Returns NULL if str is NULL. 如果str为NULL，则返回NULL。ASCII() works for 8-bit characters.ASCII()适用于8位字符。

mysql> SELECT ASCII('2');
        -> 50
mysql> SELECT ASCII(2);
        -> 50
mysql> SELECT ASCII('dx');
        -> 100

See also the ORD() function.另请参见ORD()函数。

BIN(N)

Returns a string representation of the binary value of N, where N is a longlong (BIGINT) number. 返回二进制值N的字符串表示形式，其中N是longlong（BIGINT）数。This is equivalent to CONV(N,10,2). 这相当于CONV(N,10,2)。Returns NULL if N is NULL.如果N为NULL，则返回NULL。

mysql> SELECT BIN(12);
        -> '1100'

BIT_LENGTH(str)

Returns the length of the string str in bits.返回字符串str的长度（位）。

mysql> SELECT BIT_LENGTH('text');
        -> 32

CHAR(N,... [USING charset_name])

CHAR() interprets each argument N as an integer and returns a string consisting of the characters given by the code values of those integers. NULL values are skipped.CHAR()将每个参数N解释为一个整数，并返回由这些整数的代码值给定的字符组成的字符串。跳过空值。

mysql> SELECT CHAR(77,121,83,81,'76');
        -> 'MySQL'
mysql> SELECT CHAR(77,77.3,'77.3');
        -> 'MMM'

CHAR() arguments larger than 255 are converted into multiple result bytes. 大于255的CHAR()参数将转换为多个结果字节。For example, CHAR(256) is equivalent to CHAR(1,0), and CHAR(256*256) is equivalent to CHAR(1,0,0):例如，CHAR(256)等价于CHAR(1,0)，CHAR(256*256)等价于CHAR(1,0,0)：

mysql> SELECT HEX(CHAR(1,0)), HEX(CHAR(256));
+----------------+----------------+
| HEX(CHAR(1,0)) | HEX(CHAR(256)) |
+----------------+----------------+
| 0100           | 0100           |
+----------------+----------------+
mysql> SELECT HEX(CHAR(1,0,0)), HEX(CHAR(256*256));
+------------------+--------------------+
| HEX(CHAR(1,0,0)) | HEX(CHAR(256*256)) |
+------------------+--------------------+
| 010000           | 010000             |
+------------------+--------------------+

By default, CHAR() returns a binary string. 默认情况下，CHAR()返回一个二进制字符串。To produce a string in a given character set, use the optional USING clause:要在给定的字符集中生成字符串，请使用可选的USING子句：

mysql> SELECT CHARSET(CHAR(X'65')), CHARSET(CHAR(X'65' USING utf8));
+----------------------+---------------------------------+
| CHARSET(CHAR(X'65')) | CHARSET(CHAR(X'65' USING utf8)) |
+----------------------+---------------------------------+
| binary               | utf8                            |
+----------------------+---------------------------------+

If USING is given and the result string is illegal for the given character set, a warning is issued. 如果给定USING并且结果字符串对于给定的字符集是非法的，则发出警告。Also, if strict SQL mode is enabled, the result from CHAR() becomes NULL.此外，如果启用了严格SQL模式，CHAR()的结果将变为NULL。

If CHAR() is invoked from within the mysql client, binary strings display using hexadecimal notation, depending on the value of the --binary-as-hex. 如果从mysql客户机中调用CHAR()，则二进制字符串将使用十六进制表示法显示，具体取决于--binary-as-hex的值。For more information about that option, see Section 4.5.1, “mysql — The MySQL Command-Line Client”.有关该选项的更多信息，请参阅第4.5.1节，“mysql命令行客户端”。

CHAR_LENGTH(str)

Returns the length of the string str, measured in characters. 返回字符串str的长度，以字符为单位。A multibyte character counts as a single character. 多字节字符计为单个字符。This means that for a string containing five 2-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5.这意味着，对于包含五个2字节字符的字符串，LENGTH()返回10，而CHAR_LENGTH()返回5。

CHARACTER_LENGTH(str)

CHARACTER_LENGTH() is a synonym for CHAR_LENGTH().CHARACTER_LENGTH()是CHAR_LENGTH()的同义词。

CONCAT(str1,str2,...)

Returns the string that results from concatenating the arguments. May have one or more arguments. 返回连接参数所产生的字符串。可能有一个或多个参数。If all arguments are nonbinary strings, the result is a nonbinary string. 如果所有参数都是非二进制字符串，则结果是非二进制字符串。If the arguments include any binary strings, the result is a binary string. 如果参数包含任何二进制字符串，则结果是二进制字符串。A numeric argument is converted to its equivalent nonbinary string form.数值参数将转换为其等效的非二进制字符串形式。

CONCAT() returns NULL if any argument is NULL.如果任一参数为NULL，CONCAT()将返回NULL。

mysql> SELECT CONCAT('My', 'S', 'QL');
        -> 'MySQL'
mysql> SELECT CONCAT('My', NULL, 'QL');
        -> NULL
mysql> SELECT CONCAT(14.3);
        -> '14.3'

For quoted strings, concatenation can be performed by placing the strings next to each other:对于带引号的字符串，可以通过将字符串相邻放置来执行串联：

mysql> SELECT 'My' 'S' 'QL';
        -> 'MySQL'

If CONCAT() is invoked from within the mysql client, binary string results display using hexadecimal notation, depending on the value of the --binary-as-hex. 如果从mysql客户机中调用CONCAT()，则二进制字符串结果将使用十六进制表示法显示，具体取决于--binary-as-hex的值。For more information about that option, see Section 4.5.1, “mysql — The MySQL Command-Line Client”.有关该选项的更多信息，请参阅第4.5.1节，“mysql命令行客户端”。

CONCAT_WS(separator,str1,str2,...)

CONCAT_WS() stands for Concatenate With Separator and is a special form of CONCAT(). CONCAT_WS()表示用分隔符连接，是CONCAT()的一种特殊形式。The first argument is the separator for the rest of the arguments. 第一个参数是其余参数的分隔符。The separator is added between the strings to be concatenated. 分隔符添加在要连接的字符串之间。The separator can be a string, as can the rest of the arguments. 分隔符可以是字符串，其他参数也可以是字符串。If the separator is NULL, the result is NULL.如果分隔符为NULL，则结果为NULL。

mysql> SELECT CONCAT_WS(',','First name','Second name','Last Name');
        -> 'First name,Second name,Last Name'
mysql> SELECT CONCAT_WS(',','First name',NULL,'Last Name');
        -> 'First name,Last Name'

CONCAT_WS() does not skip empty strings. 不跳过空字符串。However, it does skip any NULL values after the separator argument.但是，它会跳过分隔符参数之后的任何NULL值。

ELT(N,str1,str2,str3,...)

ELT() returns the Nth element of the list of strings: str1 if N = 1, str2 if N = 2, and so on. ELT()返回字符串列表的第N个元素：如果N = 1，则返回str1；如果N = 2，则返回str2，依此类推。Returns NULL if N is less than 1 or greater than the number of arguments. 如果N小于1或大于参数数目，则返回NULL。ELT() is the complement of FIELD().ELT()是FIELD()的补码。

mysql> SELECT ELT(1, 'Aa', 'Bb', 'Cc', 'Dd');
        -> 'Aa'
mysql> SELECT ELT(4, 'Aa', 'Bb', 'Cc', 'Dd');
        -> 'Dd'

EXPORT_SET(bits,on,off[,separator[,number_of_bits]])

Returns a string such that for every bit set in the value bits, you get an on string and for every bit not set in the value, you get an off string. 返回一个字符串，这样对于值位中设置的每一位，您都会得到一个on字符串，对于值中未设置的每一位，您都会得到一个off字符串。Bits in bits are examined from right to left (from low-order to high-order bits). 从右到左（从低位到高位）检查bits中的位。Strings are added to the result from left to right, separated by the separator string (the default being the comma character ,). 字符串从左到右添加到结果中，由separator字符串分隔（默认为逗号字符,）。The number of bits examined is given by number_of_bits, which has a default of 64 if not specified. 检查的位数由number_of_bits给出，如果未指定，则默认值为64。number_of_bits is silently clipped to 64 if larger than 64. 如果大于64，则number_of_bits将自动剪裁为64。It is treated as an unsigned integer, so a value of −1 is effectively the same as 64.它被视为无符号整数，因此值-1实际上与64相同。

mysql> SELECT EXPORT_SET(5,'Y','N',',',4);
        -> 'Y,N,Y,N'
mysql> SELECT EXPORT_SET(6,'1','0',',',10);
        -> '0,1,1,0,0,0,0,0,0,0'

FIELD(str,str1,str2,str3,...)

Returns the index (position) of str in the str1, str2, str3, ... list. 返回str在str1、str2、str3……列表中的索引（位置）。Returns 0 if str is not found.如果找不到str，则返回0。

If all arguments to FIELD() are strings, all arguments are compared as strings. 如果FIELD()的所有参数都是字符串，则将所有参数作为字符串进行比较。If all arguments are numbers, they are compared as numbers. 如果所有参数都是数字，则它们将作为数字进行比较。Otherwise, the arguments are compared as double.否则，参数将作为双参数进行比较。

If str is NULL, the return value is 0 because NULL fails equality comparison with any value. 如果str为NULL，则返回值为0，因为NULL无法与任何值进行相等比较。FIELD() is the complement of ELT().FIELD()是ELT()的补码。

mysql> SELECT FIELD('Bb', 'Aa', 'Bb', 'Cc', 'Dd', 'Ff');
        -> 2
mysql> SELECT FIELD('Gg', 'Aa', 'Bb', 'Cc', 'Dd', 'Ff');
        -> 0

FIND_IN_SET(str,strlist)

Returns a value in the range of 1 to N if the string str is in the string list strlist consisting of N substrings. 如果字符串str位于由N个子字符串组成的字符串列表strlist中，则返回1到N之间的值。A string list is a string composed of substrings separated by , characters. 字符串列表是一个由,字符分隔的子字符串组成的字符串。If the first argument is a constant string and the second is a column of type SET, the FIND_IN_SET() function is optimized to use bit arithmetic. 如果第一个参数是常量字符串，第二个参数是SET类型的列，则FIND_IN_SET()函数将优化为使用位算术。Returns 0 if str is not in strlist or if strlist is the empty string. 如果str不在strlist中，或strlist是空字符串，则返回0。Returns NULL if either argument is NULL. 如果任一参数为NULL，则返回NULL。This function does not work properly if the first argument contains a comma (,) character.如果第一个参数包含逗号（,）字符，则此函数无法正常工作。

mysql> SELECT FIND_IN_SET('b','a,b,c,d');
        -> 2

FORMAT(X,D[,locale])

Formats the number X to a format like '#,###,###.##', rounded to D decimal places, and returns the result as a string. 将数字X格式化为'#,###,###.##'等格式，四舍五入到D位小数，并以字符串形式返回结果。If D is 0, the result has no decimal point or fractional part.如果D为0，则结果没有小数点或小数部分。

The optional third parameter enables a locale to be specified to be used for the result number's decimal point, thousands separator, and grouping between separators. 可选的第三个参数允许指定区域设置，以用于结果数字的小数点、千位分隔符和分隔符之间的分组。Permissible locale values are the same as the legal values for the lc_time_names system variable (see Section 10.16, “MySQL Server Locale Support”). 允许的区域设置值与lc_time_names系统变量的合法值相同（请参阅第10.16节，“MySQL服务器区域设置支持”）。If no locale is specified, the default is 'en_US'.如果未指定区域设置，则默认值为'en_US'。

mysql> SELECT FORMAT(12332.123456, 4);
        -> '12,332.1235'
mysql> SELECT FORMAT(12332.1,4);
        -> '12,332.1000'
mysql> SELECT FORMAT(12332.2,0);
        -> '12,332'
mysql> SELECT FORMAT(12332.2,2,'de_DE');
        -> '12.332,20'

FROM_BASE64(str)

Takes a string encoded with the base-64 encoded rules used by TO_BASE64() and returns the decoded result as a binary string. 获取用TO_BASE64()使用的base-64编码规则编码的字符串，并将解码结果作为二进制字符串返回。The result is NULL if the argument is NULL or not a valid base-64 string. 如果参数为NULL或不是有效的base-64字符串，则结果为NULL。See the description of TO_BASE64() for details about the encoding and decoding rules.有关编码和解码规则的详细信息，请参阅TO_BASE64()的说明。

mysql> SELECT TO_BASE64('abc'), FROM_BASE64(TO_BASE64('abc'));
        -> 'JWJj', 'abc'

If FROM_BASE64() is invoked from within the mysql client, binary strings display using hexadecimal notation, depending on the value of the --binary-as-hex. 如果从mysql客户机中调用FROM_BASE64()，则二进制字符串将使用十六进制表示法显示，具体取决于--binary-as-hex的值。For more information about that option, see Section 4.5.1, “mysql — The MySQL Command-Line Client”.有关该选项的更多信息，请参阅第4.5.1节，“mysql命令行客户端”。

HEX(str), HEX(N)

For a string argument str, HEX() returns a hexadecimal string representation of str where each byte of each character in str is converted to two hexadecimal digits. 对于字符串参数str，HEX()返回str的十六进制字符串表示形式，其中str中每个字符的每个字节都转换为两个十六进制数字。(Multibyte characters therefore become more than two digits.) （因此，多字节字符会变成两位数以上。）The inverse of this operation is performed by the UNHEX() function.此操作的逆操作由UNHEX()函数执行。

For a numeric argument N, HEX() returns a hexadecimal string representation of the value of N treated as a longlong (BIGINT) number. 对于数值参数N，HEX()返回N值的十六进制字符串表示形式，N值被视为longlong（BIGINT）数字。This is equivalent to CONV(N,10,16). 这相当于CONV(N,10,16)。The inverse of this operation is performed by CONV(HEX(N),16,10).此操作的逆操作由CONV(HEX(N),16,10)执行。

mysql> SELECT X'616263', HEX('abc'), UNHEX(HEX('abc'));
        -> 'abc', 616263, 'abc'
mysql> SELECT HEX(255), CONV(HEX(255),16,10);
        -> 'FF', 255

INSERT(str,pos,len,newstr)

Returns the string str, with the substring beginning at position pos and len characters long replaced by the string newstr. 返回字符串str，子字符串从位置pos开始，len个字符由字符串newstr替换。Returns the original string if pos is not within the length of the string. 如果pos不在字符串长度内，则返回原始字符串。Replaces the rest of the string from position pos if len is not within the length of the rest of the string. 如果len不在字符串其余部分的长度内，则从位置pos替换字符串其余部分。Returns NULL if any argument is NULL.如果任一参数为NULL，则返回NULL。

mysql> SELECT INSERT('Quadratic', 3, 4, 'What');
        -> 'QuWhattic'
mysql> SELECT INSERT('Quadratic', -1, 4, 'What');
        -> 'Quadratic'
mysql> SELECT INSERT('Quadratic', 3, 100, 'What');
        -> 'QuWhat'

This function is multibyte safe.此函数是多字节安全的。

INSTR(str,substr)

Returns the position of the first occurrence of substring substr in string str. 返回字符串str中第一个出现的子字符串substr的位置。This is the same as the two-argument form of LOCATE(), except that the order of the arguments is reversed.这与LOCATE()的双参数形式相同，只是参数的顺序相反。

mysql> SELECT INSTR('foobarbar', 'bar');
        -> 4
mysql> SELECT INSTR('xbar', 'foobar');
        -> 0

This function is multibyte safe, and is case-sensitive only if at least one argument is a binary string.此函数是多字节安全的，并且仅当至少有一个参数是二进制字符串时才区分大小写。

LCASE(str)

LCASE() is a synonym for LOWER().LCASE()是LOWER()的同义词。

LCASE() used in a view is rewritten as LOWER() when storing the view's definition. 在存储视图定义时，视图中使用的LCASE()被重写为LOWER()。(Bug #12844279)

LEFT(str,len)

Returns the leftmost len characters from the string str, or NULL if any argument is NULL.返回字符串str中最左边的len字符，如果任何参数为NULL，则返回NULL。

mysql> SELECT LEFT('foobarbar', 5);
        -> 'fooba'

This function is multibyte safe.此函数是多字节安全的。

LENGTH(str)

Returns the length of the string str, measured in bytes. 返回字符串str的长度，以字节为单位。A multibyte character counts as multiple bytes. 多字节字符计为多字节。This means that for a string containing five 2-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5.这意味着，对于包含五个2字节字符的字符串，LENGTH()返回10，而CHAR_LENGTH()返回5。

mysql> SELECT LENGTH('text');
        -> 4

LOAD_FILE(file_name)

Reads the file and returns the file contents as a string. 读取文件并以字符串形式返回文件内容。To use this function, the file must be located on the server host, you must specify the full path name to the file, and you must have the FILE privilege. 要使用此功能，文件必须位于服务器主机上，必须指定文件的完整路径名，并且必须具有FILE权限。The file must be readable by the server and its size less than max_allowed_packet bytes. 文件必须可被服务器读取，并且其大小小于max_allowed_packet字节数。If the secure_file_priv system variable is set to a nonempty directory name, the file to be loaded must be located in that directory. 如果secure_file_priv系统变量设置为非空目录名，则要加载的文件必须位于该目录中。(Prior to MySQL 8.0.17, the file must be readable by all, not just readable by the server.)（在MySQL8.0.17之前，文件必须是所有人都可读的，而不仅仅是服务器可读的。）

If the file does not exist or cannot be read because one of the preceding conditions is not satisfied, the function returns NULL.如果文件不存在或由于不满足上述条件之一而无法读取，则函数将返回NULL。

The character_set_filesystem system variable controls interpretation of file names that are given as literal strings.character_set_filesystem系统变量控制以文本字符串形式给出的文件名的解释。

mysql> UPDATE t
  SET blob_col=LOAD_FILE('/tmp/picture')
  WHERE id=1;

LOCATE(substr,str), LOCATE(substr,str,pos)

The first syntax returns the position of the first occurrence of substring substr in string str. 第一种语法返回字符串str中第一个出现的子字符串substr的位置。The second syntax returns the position of the first occurrence of substring substr in string str, starting at position pos. 第二种语法返回字符串str中从pos开始，第一个出现的子字符串substr的位置。Returns 0 if substr is not in str. 如果substr不在str中，则返回0。Returns NULL if any argument is NULL.如果任一参数为NULL，则返回NULL。

mysql> SELECT LOCATE('bar', 'foobarbar');
        -> 4
mysql> SELECT LOCATE('xbar', 'foobar');
        -> 0
mysql> SELECT LOCATE('bar', 'foobarbar', 5);
        -> 7

This function is multibyte safe, and is case-sensitive only if at least one argument is a binary string.此函数是多字节安全的，并且仅当至少有一个参数是二进制字符串时才区分大小写。

LOWER(str)

Returns the string str with all characters changed to lowercase according to the current character set mapping. 返回字符串str，其中所有字符根据当前字符集映射更改为小写。The default is utf8mb4.默认值为utf8mb4。

mysql> SELECT LOWER('QUADRATICALLY');
        -> 'quadratically'

LOWER() (and UPPER()) are ineffective when applied to binary strings (BINARY, VARBINARY, BLOB). 应用于二进制字符串（BINARY、VARBINARY、BLOB）时，LOWER()（和UPPER()）无效。To perform lettercase conversion of a binary string, first convert it to a nonbinary string using a character set appropriate for the data stored in the string:要执行二进制字符串的字母大小写转换，请首先使用适合字符串中存储的数据的字符集将其转换为非二进制字符串：

mysql> SET @str = BINARY 'New York';
mysql> SELECT LOWER(@str), LOWER(CONVERT(@str USING utf8mb4));
+-------------+------------------------------------+
| LOWER(@str) | LOWER(CONVERT(@str USING utf8mb4)) |
+-------------+------------------------------------+
| New York    | new york                           |
+-------------+------------------------------------+

For collations of Unicode character sets, LOWER() and UPPER() work according to the Unicode Collation Algorithm (UCA) version in the collation name, if there is one, and UCA 4.0.0 if no version is specified. 对于Unicode字符集的排序规则，LOWER()和UPPER()根据排序规则名称中的Unicode排序规则算法（UCA)版本（如果有）工作，如果没有指定版本，则根据UCA 4.0.0工作。For example, utf8mb4_0900_ai_ci and utf8_unicode_520_ci work according to UCA 9.0.0 and 5.2.0, respectively, whereas utf8_unicode_ci works according to UCA 4.0.0. 例如，utf8mb4_0900_ai_ci和utf8_unicode_520_ci分别根据UCA 9.0.0和5.2.0工作，而utf8_unicode_ci根据UCA 4.0.0工作。See Section 10.10.1, “Unicode Character Sets”.请参阅第10.10.1节，“Unicode字符集”。

This function is multibyte safe.此函数是多字节安全的。

LCASE() used within views is rewritten as LOWER().视图中使用的LCASE()被重写为LOWER()。

LPAD(str,len,padstr)

Returns the string str, left-padded with the string padstr to a length of len characters. 返回字符串str，用字符串padstr左填充，长度为len个字符。If str is longer than len, the return value is shortened to len characters.如果str长于len，则返回值将缩短为len个字符。

mysql> SELECT LPAD('hi',4,'??');
        -> '??hi'
mysql> SELECT LPAD('hi',1,'??');
        -> 'h'

LTRIM(str)

Returns the string str with leading space characters removed.返回删除前导空格字符的字符串str。

mysql> SELECT LTRIM('  barbar');
        -> 'barbar'

This function is multibyte safe.此函数是多字节安全的。

MAKE_SET(bits,str1,str2,...)

Returns a set value (a string containing substrings separated by , characters) consisting of the strings that have the corresponding bit in bits set. 返回一个集值（一个包含由字符,分隔的子字符串的字符串），该字符串由bits集中具有相应位的字符串组成。str1 corresponds to bit 0, str2 to bit 1, and so on. str1对应于位0，str2对应于位1，依此类推。NULL values in str1, str2, ... are not appended to the result.str1、str2……不会附加到结果。

mysql> SELECT MAKE_SET(1,'a','b','c');
        -> 'a'
mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world');
        -> 'hello,world'
mysql> SELECT MAKE_SET(1 | 4,'hello','nice',NULL,'world');
        -> 'hello'
mysql> SELECT MAKE_SET(0,'a','b','c');
        -> ''

MID(str,pos,len)

MID(str,pos,len) is a synonym for SUBSTRING(str,pos,len).MID(str,pos,len)是SUBSTRING(str,pos,len)的同义词。

OCT(N)

Returns a string representation of the octal value of N, where N is a longlong (BIGINT) number. 返回N的八进制值的字符串表示形式，其中N是longlong（BIGINT）数。This is equivalent to CONV(N,10,8). 这相当于CONV(N,10,8)。Returns NULL if N is NULL.如果N为NULL，则返回NULL。

mysql> SELECT OCT(12);
        -> '14'

OCTET_LENGTH(str)

OCTET_LENGTH() is a synonym for LENGTH().OCTET_LENGTH()是LENGTH()的同义词。

ORD(str)

If the leftmost character of the string str is a multibyte character, returns the code for that character, calculated from the numeric values of its constituent bytes using this formula:如果字符串str的最左边的字符是多字节字符，则返回该字符的代码，使用以下公式从其组成字节的数值计算得出：

  (1st byte code)
+ (2nd byte code * 256)
+ (3rd byte code * 256^2) ...

If the leftmost character is not a multibyte character, ORD() returns the same value as the ASCII() function.如果最左边的字符不是多字节字符，ORD()将返回与ASCII()函数相同的值。

mysql> SELECT ORD('2');
        -> 50

POSITION(substr IN str)

POSITION(substr IN str) is a synonym for LOCATE(substr,str).

QUOTE(str)

Quotes a string to produce a result that can be used as a properly escaped data value in an SQL statement. 引用字符串以生成一个结果，该结果可用作SQL语句中正确转义的数据值。The string is returned enclosed by single quotation marks and with each instance of backslash (\), single quote ('), ASCII NUL, and Control+Z preceded by a backslash. 返回的字符串用单引号括起来，每个反斜杠（\）、单引号（'）、ASCII NUL和Control+Z实例前面都有一个反斜杠。If the argument is NULL, the return value is the word “NULL” without enclosing single quotation marks.如果参数为NULL，则返回值为单词“NULL”，不包含单引号。

mysql> SELECT QUOTE('Don\'t!');
        -> 'Don\'t!'
mysql> SELECT QUOTE(NULL);
        -> NULL

For comparison, see the quoting rules for literal strings and within the C API in Section 9.1.1, “String Literals”, and mysql_real_escape_string_quote().要进行比较，请参阅第9.1.1节，“字符串文本”中的文字字符串和C API内的引号规则和mysql_real_escape_String_quote()。

REPEAT(str,count)

Returns a string consisting of the string str repeated count times. 返回由字符串str重复count次数组成的字符串。If count is less than 1, returns an empty string. 如果count小于1，则返回空字符串。Returns NULL if str or count are NULL.如果str或count为NULL，则返回NULL。

mysql> SELECT REPEAT('MySQL', 3);
        -> 'MySQLMySQLMySQL'

REPLACE(str,from_str,to_str)

Returns the string str with all occurrences of the string from_str replaced by the string to_str. 返回字符串str，其中所有出现的字符串from_str替换为字符串to_str。REPLACE() performs a case-sensitive match when searching for from_str.REPLACE()在搜索from_str时执行区分大小写的匹配。

mysql> SELECT REPLACE('www.mysql.com', 'w', 'Ww');
        -> 'WwWwWw.mysql.com'

This function is multibyte safe.此函数是多字节安全的。

REVERSE(str)

Returns the string str with the order of the characters reversed.返回字符顺序颠倒的字符串str。

mysql> SELECT REVERSE('abc');
        -> 'cba'

This function is multibyte safe.此函数是多字节安全的。

RIGHT(str,len)

Returns the rightmost len characters from the string str, or NULL if any argument is NULL.返回字符串str中最右边的len字符，如果任何参数为NULL，则返回NULL。

mysql> SELECT RIGHT('foobarbar', 4);
        -> 'rbar'

This function is multibyte safe.此函数是多字节安全的。

RPAD(str,len,padstr)

Returns the string str, right-padded with the string padstr to a length of len characters. 返回字符串str，用字符串padstr右填充，长度为len个字符。If str is longer than len, the return value is shortened to len characters.如果str长于len，则返回值将缩短为len个字符。

mysql> SELECT RPAD('hi',5,'?');
        -> 'hi???'
mysql> SELECT RPAD('hi',1,'?');
        -> 'h'

This function is multibyte safe.此函数是多字节安全的。

RTRIM(str)

Returns the string str with trailing space characters removed.返回删除了尾随空格字符的字符串str。

mysql> SELECT RTRIM('barbar   ');
        -> 'barbar'

This function is multibyte safe.此函数是多字节安全的。

SOUNDEX(str)

Returns a soundex string from str. 从str返回soundex字符串。Two strings that sound almost the same should have identical soundex strings. 两个声音几乎相同的弦应该有相同的soundex弦。A standard soundex string is four characters long, but the SOUNDEX() function returns an arbitrarily long string. 标准的soundex字符串有四个字符长，但是SOUNDEX()函数返回任意长的字符串。You can use SUBSTRING() on the result to get a standard soundex string. 可以对结果使用SUBSTRING()来获取标准的soundex字符串。All nonalphabetic characters in str are ignored. str中的所有非字母字符都被忽略。All international alphabetic characters outside the A-Z range are treated as vowels.A-Z范围以外的所有国际字母字符都被视为元音。

mysql> SELECT SOUNDEX('Hello');
        -> 'H400'
mysql> SELECT SOUNDEX('Quadratically');
        -> 'Q36324'

expr1 SOUNDS LIKE expr2

This is the same as SOUNDEX(expr1) = SOUNDEX(expr2).这相当于SOUNDEX(expr1) = SOUNDEX(expr2)。

SPACE(N)

Returns a string consisting of N space characters.返回由N个空格字符组成的字符串。

mysql> SELECT SPACE(6);
        -> '      '

SUBSTR(str,pos), SUBSTR(str FROM pos), SUBSTR(str,pos,len), SUBSTR(str FROM pos FOR len)

SUBSTR() is a synonym for SUBSTRING().SUBSTR()是SUBSTRING()的同义词。

SUBSTRING(str,pos), SUBSTRING(str FROM pos), SUBSTRING(str,pos,len), SUBSTRING(str FROM pos FOR len)

The forms without a len argument return a substring from string str starting at position pos. 不带len参数的形式从位置pos开始返回字符串str的子字符串。The forms with a len argument return a substring len characters long from string str, starting at position pos. 带有len参数的形式返回字符串str中长度为len个字符的子字符串，从位置pos开始。The forms that use FROM are standard SQL syntax. 使用FROM的形式是标准的SQL语法。It is also possible to use a negative value for pos. pos也可以使用负值。In this case, the beginning of the substring is pos characters from the end of the string, rather than the beginning. 在本例中，子字符串的开头是从字符串末尾开始数pos字符，而不是从开头开始数。A negative value may be used for pos in any of the forms of this function. 此函数的任何形式的pos都可以使用负值。A value of 0 for pos returns an empty string.pos的值为0将返回空字符串。

For all forms of SUBSTRING(), the position of the first character in the string from which the substring is to be extracted is reckoned as 1.对于SUBSTRING()的所有形式，要从中提取子字符串的字符串中第一个字符的位置都被认为是1。

mysql> SELECT SUBSTRING('Quadratically',5);
        -> 'ratically'
mysql> SELECT SUBSTRING('foobarbar' FROM 4);
        -> 'barbar'
mysql> SELECT SUBSTRING('Quadratically',5,6);
        -> 'ratica'
mysql> SELECT SUBSTRING('Sakila', -3);
        -> 'ila'
mysql> SELECT SUBSTRING('Sakila', -5, 3);
        -> 'aki'
mysql> SELECT SUBSTRING('Sakila' FROM -4 FOR 2);
        -> 'ki'

This function is multibyte safe.此函数是多字节安全的。

If len is less than 1, the result is the empty string.如果len小于1，则结果为空字符串。

SUBSTRING_INDEX(str,delim,count)

Returns the substring from string str before count occurrences of the delimiter delim. 在分隔符delim出现计数之前，返回字符串str中的子字符串。If count is positive, everything to the left of the final delimiter (counting from the left) is returned. 如果count为正，则返回最后定界符左侧的所有内容（从左侧开始计数）。If count is negative, everything to the right of the final delimiter (counting from the right) is returned. 如果count为负数，则返回最后定界符右侧的所有内容（从右侧开始计数）。SUBSTRING_INDEX() performs a case-sensitive match when searching for delim.SUBSTRING_INDEX()在搜索delim时执行区分大小写的匹配。

mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', 2);
        -> 'www.mysql'
mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', -2);
        -> 'mysql.com'

This function is multibyte safe.此函数是多字节安全的。

TO_BASE64(str)

Converts the string argument to base-64 encoded form and returns the result as a character string with the connection character set and collation. 将字符串参数转换为base-64编码形式，并将结果作为包含连接字符集和排序规则的字符串返回。If the argument is not a string, it is converted to a string before conversion takes place. 如果参数不是字符串，则在转换之前将其转换为字符串。The result is NULL if the argument is NULL. 如果参数为NULL，则结果为NULL。Base-64 encoded strings can be decoded using the FROM_BASE64() function.Base-64编码的字符串可以使用FROM_BASE64()函数进行解码。

mysql> SELECT TO_BASE64('abc'), FROM_BASE64(TO_BASE64('abc'));
        -> 'JWJj', 'abc'

Different base-64 encoding schemes exist. 存在不同的base-64编码方案。These are the encoding and decoding rules used by TO_BASE64() and FROM_BASE64():以下是TO_BASE64()和FROM_BASE64()使用的编码和解码规则：

TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str), TRIM([remstr FROM] str)

Returns the string str with all remstr prefixes or suffixes removed. 返回删除了所有remstr前缀或后缀的字符串str。If none of the specifiers BOTH, LEADING, or TRAILING is given, BOTH is assumed. 如果没有同时给定任何说明符BOTH、LEADING或TRAILING，则假定两者都是。remstr is optional and, if not specified, spaces are removed.remstr是可选的，如果未指定，则删除空格。

mysql> SELECT TRIM('  bar   ');
        -> 'bar'
mysql> SELECT TRIM(LEADING 'x' FROM 'xxxbarxxx');
        -> 'barxxx'
mysql> SELECT TRIM(BOTH 'x' FROM 'xxxbarxxx');
        -> 'bar'
mysql> SELECT TRIM(TRAILING 'xyz' FROM 'barxxyz');
        -> 'barx'

This function is multibyte safe.此函数是多字节安全的。

UCASE(str)

UCASE() is a synonym for UPPER().UCASE()是UPPER()的同义词。

UCASE() used within views is rewritten as UPPER().视图中使用的UCASE()被重写为UPPER()。

UNHEX(str)

For a string argument str, UNHEX(str) interprets each pair of characters in the argument as a hexadecimal number and converts it to the byte represented by the number. 对于字符串参数str，UNHEX(str)将参数中的每对字符解释为十六进制数，并将其转换为该数字表示的字节。The return value is a binary string.返回值是二进制字符串。

mysql> SELECT UNHEX('4D7953514C');
        -> 'MySQL'
mysql> SELECT X'4D7953514C';
        -> 'MySQL'
mysql> SELECT UNHEX(HEX('string'));
        -> 'string'
mysql> SELECT HEX(UNHEX('1267'));
        -> '1267'

The characters in the argument string must be legal hexadecimal digits: '0' .. '9', 'A' .. 'F', 'a' .. 'f'. 参数字符串中的字符必须是合法的十六进制数字：'0' .. '9'、'A' .. 'F'、'a' .. 'f'。If the argument contains any nonhexadecimal digits, the result is NULL:如果参数包含任何非十六进制数字，则结果为NULL：

mysql> SELECT UNHEX('GG');
+-------------+
| UNHEX('GG') |
+-------------+
| NULL        |
+-------------+

A NULL result can occur if the argument to UNHEX() is a BINARY column, because values are padded with 0x00 bytes when stored but those bytes are not stripped on retrieval. 如果UNHEX()的参数是BINARY列，则会出现NULL结果，因为存储时会用0x00字节填充值，但在检索时不会剥离这些字节。For example, '41' is stored into a CHAR(3) column as '41 ' and retrieved as '41' (with the trailing pad space stripped), so UNHEX() for the column value returns X'41'. 例如，'41'作为'41 '存储在CHAR(3)列中并检索为'41'（去掉尾随填充空格），因此列值的UNHEX()返回X'41'。By contrast, '41' is stored into a BINARY(3) column as '41\0' and retrieved as '41\0' (with the trailing pad 0x00 byte not stripped). 相比之下，'41'作为'41\0'存储在BINARY(3)列中，并作为'41\0'检索（尾部填充0x00字节未剥离）。'\0' is not a legal hexadecimal digit, so UNHEX() for the column value returns NULL.'\0'不是合法的十六进制数字，因此列值的UNHEX()返回NULL。

For a numeric argument N, the inverse of HEX(N) is not performed by UNHEX(). 对于数值参数N，UNHEX()不执行HEX(N)的逆运算。Use CONV(HEX(N),16,10) instead. 请改用CONV(HEX(N),16,10)。See the description of HEX().请参见HEX()的说明。

If UNHEX() is invoked from within the mysql client, binary strings display using hexadecimal notation, depending on the value of the --binary-as-hex. 如果从mysql客户机中调用UNHEX()，则二进制字符串将使用十六进制表示法显示，具体取决于--binary-as-hex的值。For more information about that option, see Section 4.5.1, “mysql — The MySQL Command-Line Client”.有关该选项的更多信息，请参阅第4.5.1节，“mysql命令行客户端”。

UPPER(str)

Returns the string str with all characters changed to uppercase according to the current character set mapping. 返回字符串str，其中所有字符根据当前字符集映射更改为大写。The default is utf8mb4.默认值为utf8mb4。

mysql> SELECT UPPER('Hej');
        -> 'HEJ'

See the description of LOWER() for information that also applies to UPPER(). 有关同样适用于UPPER()的信息，请参见LOWER()的说明。This included information about how to perform lettercase conversion of binary strings (BINARY, VARBINARY, BLOB) for which these functions are ineffective, and information about case folding for Unicode character sets.这包括有关如何对这些函数无效的二进制字符串（BINARY、VARBINARY、BLOB）执行字母大小写转换的信息，以及有关Unicode字符集的大小写折叠的信息。

This function is multibyte safe.此函数是多字节安全的。

UCASE() used within views is rewritten as UPPER().视图中使用的UCASE()被重写为UPPER()。

WEIGHT_STRING(str [AS {CHAR|BINARY}(N)] [flags])

This function returns the weight string for the input string. 此函数返回输入字符串的权重字符串。The return value is a binary string that represents the comparison and sorting value of the string. 返回值是一个二进制字符串，表示字符串的比较和排序值。It has these properties:它具有以下特性：

WEIGHT_STRING() is a debugging function intended for internal use. WEIGHT_STRING()是供内部使用的调试函数。Its behavior can change without notice between MySQL versions. 在MySQL版本之间，它的行为可以在没有通知的情况下更改。It can be used for testing and debugging of collations, especially if you are adding a new collation. 它可以用于测试和调试排序规则，特别是在添加新排序规则时。See Section 10.14, “Adding a Collation to a Character Set”.请参阅第10.14节，“向字符集添加排序规则”。

This list briefly summarizes the arguments. 这个列表简要地总结了这些论点。More details are given in the discussion following the list.更多细节在下面的讨论中给出。

The input string, str, is a string expression. 输入字符串str是一个字符串表达式。If the input is a nonbinary (character) string such as a CHAR, VARCHAR, or TEXT value, the return value contains the collation weights for the string. 如果输入是非二进制（字符）字符串（如CHAR、VARCHAR或TEXT值），则返回值包含该字符串的排序规则权重。If the input is a binary (byte) string such as a BINARY, VARBINARY, or BLOB value, the return value is the same as the input (the weight for each byte in a binary string is the byte value). 如果输入是二进制（字节）字符串，如BINARY、VARBINARY或BLOB值，则返回值与输入值相同（二进制字符串中每个字节的权重为byte值）。If the input is NULL, WEIGHT_STRING() returns NULL.如果输入为NULL，WEIGHT_STRING()将返回NULL。

Examples:例如：

mysql> SET @s = _utf8mb4 'AB' COLLATE utf8mb4_0900_ai_ci;
mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+
| @s   | HEX(@s) | HEX(WEIGHT_STRING(@s)) |
+------+---------+------------------------+
| AB   | 4142    | 1C471C60               |
+------+---------+------------------------+

mysql> SET @s = _utf8mb4 'ab' COLLATE utf8mb4_0900_ai_ci;
mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+
| @s   | HEX(@s) | HEX(WEIGHT_STRING(@s)) |
+------+---------+------------------------+
| ab   | 6162    | 1C471C60               |
+------+---------+------------------------+

mysql> SET @s = CAST('AB' AS BINARY);
mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+
| @s   | HEX(@s) | HEX(WEIGHT_STRING(@s)) |
+------+---------+------------------------+
| AB   | 4142    | 4142                   |
+------+---------+------------------------+

mysql> SET @s = CAST('ab' AS BINARY);
mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+
| @s   | HEX(@s) | HEX(WEIGHT_STRING(@s)) |
+------+---------+------------------------+
| ab   | 6162    | 6162                   |
+------+---------+------------------------+

The preceding examples use HEX() to display the WEIGHT_STRING() result. 前面的示例使用HEX()来显示WEIGHT_STRING()结果。Because the result is a binary value, HEX() can be especially useful when the result contains nonprinting values, to display it in printable form:因为结果是一个二进制值，所以HEX()在结果包含非打印值时特别有用，以可打印形式显示：

mysql> SET @s = CONVERT(X'C39F' USING utf8) COLLATE utf8_czech_ci;
mysql> SELECT HEX(WEIGHT_STRING(@s));
+------------------------+
| HEX(WEIGHT_STRING(@s)) |
+------------------------+
| 0FEA0FEA               |
+------------------------+

For non-NULL return values, the data type of the value is VARBINARY if its length is within the maximum length for VARBINARY, otherwise the data type is BLOB.对于非NULL返回值，如果值的长度在VARBINARY的最大长度内，则该值的数据类型为VARBINARY，否则该数据类型为BLOB。

The AS clause may be given to cast the input string to a nonbinary or binary string and to force it to a given length:AS子句可用于将输入字符串强制转换为非二进制或二进制字符串，并将其强制转换为给定长度：

mysql> SET NAMES 'latin1';
mysql> SELECT HEX(WEIGHT_STRING('ab' AS CHAR(4)));
+-------------------------------------+
| HEX(WEIGHT_STRING('ab' AS CHAR(4))) |
+-------------------------------------+
| 41422020                            |
+-------------------------------------+
mysql> SET NAMES 'utf8';
mysql> SELECT HEX(WEIGHT_STRING('ab' AS CHAR(4)));
+-------------------------------------+
| HEX(WEIGHT_STRING('ab' AS CHAR(4))) |
+-------------------------------------+
| 0041004200200020                    |
+-------------------------------------+

mysql> SELECT HEX(WEIGHT_STRING('ab' AS BINARY(4)));
+---------------------------------------+
| HEX(WEIGHT_STRING('ab' AS BINARY(4))) |
+---------------------------------------+
| 61620000                              |
+---------------------------------------+

The flags clause currently is unused.flags子句当前未使用。

If WEIGHT_STRING() is invoked from within the mysql client, binary strings display using hexadecimal notation, depending on the value of the --binary-as-hex. 如果从mysql客户机中调用WEIGHT_STRING()，则二进制字符串将使用十六进制表示法显示，具体取决于--binary-as-hex的值。For more information about that option, see Section 4.5.1, “mysql — The MySQL Command-Line Client”.有关该选项的更多信息，请参阅第4.5.1节，“mysql命令行客户端”。