ABS(X)

Returns the absolute value of X, or NULL if X is NULL.返回X的绝对值，如果X为NULL，则返回NULL。

The result type is derived from the argument type. 结果类型派生自参数类型。An implication of this is that ABS(-9223372036854775808) produces an error because the result cannot be stored in a signed BIGINT value.这意味着ABS(-9223372036854775808)产生错误，因为结果不能存储在有符号的BIGINT值中。

mysql> SELECT ABS(2);
        -> 2
mysql> SELECT ABS(-32);
        -> 32

This function is safe to use with BIGINT values.此函数与BIGINT值一起使用是安全的。

ACOS(X)

Returns the arc cosine of X, that is, the value whose cosine is X. 返回X的弧余弦，即余弦为X的值。Returns NULL if X is not in the range -1 to 1.如果X不在-1到1的范围内，则返回NULL。

mysql> SELECT ACOS(1);
        -> 0
mysql> SELECT ACOS(1.0001);
        -> NULL
mysql> SELECT ACOS(0);
        -> 1.5707963267949

ASIN(X)

Returns the arc sine of X, that is, the value whose sine is X. 返回X的弧正弦，即正弦为X的值。Returns NULL if X is not in the range -1 to 1.如果X不在-1到1的范围内，则返回NULL。

mysql> SELECT ASIN(0.2);
        -> 0.20135792079033
mysql> SELECT ASIN('foo');

+-------------+
| ASIN('foo') |
+-------------+
|           0 |
+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> SHOW WARNINGS;
+---------+------+-----------------------------------------+
| Level   | Code | Message                                 |
+---------+------+-----------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'foo' |
+---------+------+-----------------------------------------+

ATAN(X)

Returns the arc tangent of X, that is, the value whose tangent is X.返回X的反正切值，即正切为X的值。

mysql> SELECT ATAN(2);
        -> 1.1071487177941
mysql> SELECT ATAN(-2);
        -> -1.1071487177941

ATAN(Y,X), ATAN2(Y,X)

Returns the arc tangent of the two variables X and Y. 返回两个变量X和Y的反正切值。It is similar to calculating the arc tangent of Y / X, except that the signs of both arguments are used to determine the quadrant of the result.它类似于计算Y / X的反正切，只是两个参数的符号都用来确定结果的象限。

mysql> SELECT ATAN(-2,2);
        -> -0.78539816339745
mysql> SELECT ATAN2(PI(),0);
        -> 1.5707963267949

CEIL(X)

CEIL() is a synonym for 是CEILING().的同义词。

CEILING(X)

Returns the smallest integer value not less than X.返回不小于X的最小整数值。

mysql> SELECT CEILING(1.23);
        -> 2
mysql> SELECT CEILING(-1.23);
        -> -1

For exact-value numeric arguments, the return value has an exact-value numeric type. 对于精确值数字参数，返回值具有精确值数字类型。For string or floating-point arguments, the return value has a floating-point type.对于字符串或浮点参数，返回值具有浮点类型。

CONV(N,from_base,to_base)

Converts numbers between different number bases. 在不同的基数之间转换数字。Returns a string representation of the number N, converted from base from_base to base to_base. 返回数字N的字符串表示形式，从基数from_base转换为基数to_base。Returns NULL if any argument is NULL. 如果任一参数为NULL，则返回NULL。The argument N is interpreted as an integer, but may be specified as an integer or a string. 参数N被解释为整数，但可以指定为整数或字符串。The minimum base is 2 and the maximum base is 36. 最小基数为2，最大基数为36。If from_base is a negative number, N is regarded as a signed number. 如果from_base是负数，则N被视为有符号数。Otherwise, N is treated as unsigned. 否则，N被视为无符号的。CONV() works with 64-bit precision.CONV()以64位精度工作。

mysql> SELECT CONV('a',16,2);
        -> '1010'
mysql> SELECT CONV('6E',18,8);
        -> '172'
mysql> SELECT CONV(-17,10,-18);
        -> '-H'
mysql> SELECT CONV(10+'10'+'10'+X'0a',10,10);
        -> '40'

COS(X)

Returns the cosine of X, where X is given in radians.返回X的余弦，其中X以弧度表示。

mysql> SELECT COS(PI());
        -> -1

COT(X)

Returns the cotangent of X.返回X的余切。

mysql> SELECT COT(12);
        -> -1.5726734063977
mysql> SELECT COT(0);
        -> out-of-range error

CRC32(expr)

Computes a cyclic redundancy check value and returns a 32-bit unsigned value. 计算循环冗余校验值并返回32位无符号值。The result is NULL if the argument is NULL. 如果参数为NULL，则结果为NULL。The argument is expected to be a string and (if possible) is treated as one if it is not.参数应为字符串，如果可能，则视为字符串。

mysql> SELECT CRC32('MySQL');
        -> 3259397556
mysql> SELECT CRC32('mysql');
        -> 2501908538

DEGREES(X)

Returns the argument X, converted from radians to degrees.返回参数X，从弧度转换为度。

mysql> SELECT DEGREES(PI());
        -> 180
mysql> SELECT DEGREES(PI() / 2);
        -> 90

EXP(X)

Returns the value of e (the base of natural logarithms) raised to the power of X. 返回e（自然对数的底）进行X次乘方的幂。The inverse of this function is LOG() (using a single argument only) or LN().此函数的逆函数是LOG()（仅使用单个参数）或LN()。

mysql> SELECT EXP(2);
        -> 7.3890560989307
mysql> SELECT EXP(-2);
        -> 0.13533528323661
mysql> SELECT EXP(0);
        -> 1

FLOOR(X)

Returns the largest integer value not greater than X.返回不大于X的最大整数值。

mysql> SELECT FLOOR(1.23), FLOOR(-1.23);
        -> 1, -2

For exact-value numeric arguments, the return value has an exact-value numeric type. 对于精确值数字参数，返回值具有精确值数字类型。For string or floating-point arguments, the return value has a floating-point type.对于字符串或浮点参数，返回值具有浮点类型。

FORMAT(X,D)

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'#,###,###.##'这种格式，四舍五入到D位小数，并以字符串形式返回结果。For details, see Section 12.8, “String Functions and Operators”.有关详细信息，请参阅第12.8节，“字符串函数和运算符”。

HEX(N_or_S)

This function can be used to obtain a hexadecimal representation of a decimal number or a string; the manner in which it does so varies according to the argument's type. 此函数可用于获取十进制数或字符串的十六进制表示形式；它这样做的方式因参数的类型而异。See this function's description in Section 12.8, “String Functions and Operators”, for details.有关详细信息，请参阅第12.8节，“字符串函数和运算符”中对该函数的描述。

LN(X)

Returns the natural logarithm of X; that is, the base-e logarithm of X. 返回X的自然对数；也就是X的以e为底的对数。If X is less than or equal to 0.0E0, the function returns NULL and a warning “Invalid argument for logarithm” is reported.如果X小于或等于0.0E0，则函数返回NULL并报告警告“对数参数无效”。

mysql> SELECT LN(2);
        -> 0.69314718055995
mysql> SELECT LN(-2);
        -> NULL

This function is synonymous with LOG(X). 此函数与LOG(X)函数同义。The inverse of this function is the EXP() function.此函数的逆函数是EXP()函数。

LOG(X), LOG(B,X)

If called with one parameter, this function returns the natural logarithm of X. 如果使用一个参数调用，此函数将返回X的自然对数。If X is less than or equal to 0.0E0, the function returns NULL and a warning “Invalid argument for logarithm” is reported.如果X小于或等于0.0E0，则函数返回NULL并报告警告“对数参数无效”。

The inverse of this function (when called with a single argument) is the EXP() function.此函数（使用单个参数调用时）的逆函数是EXP()函数。

mysql> SELECT LOG(2);
        -> 0.69314718055995
mysql> SELECT LOG(-2);
        -> NULL

If called with two parameters, this function returns the logarithm of X to the base B. 如果使用两个参数调用，此函数将返回X的以B为底数的对数。If X is less than or equal to 0, or if B is less than or equal to 1, then NULL is returned.如果X小于或等于0，或者如果B小于或等于1，则返回NULL。

mysql> SELECT LOG(2,65536);
        -> 16
mysql> SELECT LOG(10,100);
        -> 2
mysql> SELECT LOG(1,100);
        -> NULL

LOG(B,X) is equivalent to LOG(X) / LOG(B).

LOG2(X)

Returns the base-2 logarithm of X. 返回X的以2为底数的对数。If X is less than or equal to 0.0E0, the function returns NULL and a warning “Invalid argument for logarithm” is reported.如果X小于或等于0.0E0，则函数返回NULL并报告警告“对数参数无效”。

mysql> SELECT LOG2(65536);
        -> 16
mysql> SELECT LOG2(-100);
        -> NULL

LOG2() is useful for finding out how many bits a number requires for storage. LOG2()对于找出一个数字需要多少位来存储非常有用。This function is equivalent to the expression LOG(X) / LOG(2).此函数等效于表达式LOG(X) / LOG(2)。

LOG10(X)

Returns the base-10 logarithm of X. 返回X的以10为底数的对数。If X is less than or equal to 0.0E0, the function returns NULL and a warning “Invalid argument for logarithm” is reported.如果X小于或等于0.0E0，则函数返回NULL并报告警告“对数参数无效”。

mysql> SELECT LOG10(2);
        -> 0.30102999566398
mysql> SELECT LOG10(100);
        -> 2
mysql> SELECT LOG10(-100);
        -> NULL

LOG10(X) is equivalent to LOG(10,X).LOG10(X)等同于LOG(10,X)。

MOD(N,M), N % M, N MOD M

Modulo operation. 求模运算符。Returns the remainder of N divided by M.返回N除以M的余数。

mysql> SELECT MOD(234, 10);
        -> 4
mysql> SELECT 253 % 7;
        -> 1
mysql> SELECT MOD(29,9);
        -> 2
mysql> SELECT 29 MOD 9;
        -> 2

This function is safe to use with BIGINT values.此函数与BIGINT值一起使用是安全的。

MOD() also works on values that have a fractional part and returns the exact remainder after division:MOD()也适用于具有小数部分的值，并在除法后返回精确的余数：

mysql> SELECT MOD(34.5,3);
        -> 1.5

MOD(N,0) returns NULL.返回NULL。

PI()

Returns the value of π (pi). 返回π（圆周率）的值。The default number of decimal places displayed is seven, but MySQL uses the full double-precision value internally.默认显示的小数位数是7，但是MySQL在内部使用完整的双精度值。

mysql> SELECT PI();
        -> 3.141593
mysql> SELECT PI()+0.000000000000000000;
        -> 3.141592653589793116

POW(X,Y)

Returns the value of X raised to the power of Y.返回X的值，并将其提升为Y的幂。

mysql> SELECT POW(2,2);
        -> 4
mysql> SELECT POW(2,-2);
        -> 0.25

POWER(X,Y)

This is a synonym for POW().这是POW()的同义词。

RADIANS(X)

Returns the argument X, converted from degrees to radians. 返回参数X从度转换为弧度。(Note that π radians equals 180 degrees.)（注意π弧度等于180度。）

mysql> SELECT RADIANS(90);
        -> 1.5707963267949

RAND([N])

Returns a random floating-point value v in the range 0 <= v < 1.0. 返回一个随机浮点值v，范围为0 <= v < 1.0。To obtain a random integer R in the range i <= R < j, use the expression FLOOR(i + RAND() * (j − i)). 若要获取范围i <= R < j的随机整型数R，请使用表达式FLOOR(i + RAND() * (j - i))。For example, to obtain a random integer in the range the range 7 <= R < 12, use the following statement:例如，要获得范围为7<=R<12的随机整型数，请使用以下语句：

SELECT FLOOR(7 + (RAND() * 5));

If an integer argument N is specified, it is used as the seed value:如果指定整数参数N，则将其用作种子值：

One implication of this behavior is that for equal argument values, RAND(N) returns the same value each time, and thus produces a repeatable sequence of column values. 这种行为的一个含义是，对于相等的参数值，RAND(N)每次返回相同的值，从而生成一个可重复的列值序列。In the following example, the sequence of values produced by RAND(3) is the same both places it occurs.在下面的示例中，RAND(3)生成的值序列在两个位置都是相同的。

mysql> CREATE TABLE t (i INT);
Query OK, 0 rows affected (0.42 sec)

mysql> INSERT INTO t VALUES(1),(2),(3);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT i, RAND() FROM t;
+------+------------------+
| i    | RAND()           |
+------+------------------+
|    1 | 0.61914388706828 |
|    2 | 0.93845168309142 |
|    3 | 0.83482678498591 |
+------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT i, RAND(3) FROM t;
+------+------------------+
| i    | RAND(3)          |
+------+------------------+
|    1 | 0.90576975597606 |
|    2 | 0.37307905813035 |
|    3 | 0.14808605345719 |
+------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT i, RAND() FROM t;
+------+------------------+
| i    | RAND()           |
+------+------------------+
|    1 | 0.35877890638893 |
|    2 | 0.28941420772058 |
|    3 | 0.37073435016976 |
+------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT i, RAND(3) FROM t;
+------+------------------+
| i    | RAND(3)          |
+------+------------------+
|    1 | 0.90576975597606 |
|    2 | 0.37307905813035 |
|    3 | 0.14808605345719 |
+------+------------------+
3 rows in set (0.01 sec)

RAND() in a WHERE clause is evaluated for every row (when selecting from one table) or combination of rows (when selecting from a multiple-table join). WHERE子句中的RAND()对每一行（从一个表中选择时）或行组合（从多个表联接中选择时）求值。Thus, for optimizer purposes, RAND() is not a constant value and cannot be used for index optimizations. 因此，出于优化器的目的，RAND()不是一个常量值，不能用于索引优化。For more information, see Section 8.2.1.20, “Function Call Optimization”.有关更多信息，请参阅第8.2.1.20节，“函数调用优化”。

Use of a column with RAND() values in an ORDER BY or GROUP BY clause may yield unexpected results because for either clause a RAND() expression can be evaluated multiple times for the same row, each time returning a different result. 在ORDER BY或GROUP BY子句中使用具有RAND()值的列可能会产生意外的结果，因为对于任一子句，RAND()表达式可以对同一行进行多次求值，每次都返回不同的结果。If the goal is to retrieve rows in random order, you can use a statement like this:如果目标是按随机顺序检索行，则可以使用如下语句：

SELECT * FROM tbl_name ORDER BY RAND();

To select a random sample from a set of rows, combine ORDER BY RAND() with LIMIT:要从一组行中选择随机样本，请将ORDER BY RAND()与LIMIT结合使用：

SELECT * FROM table1, table2 WHERE a=b AND c<d ORDER BY RAND() LIMIT 1000;

RAND() is not meant to be a perfect random generator. RAND()并不是一个完美的随机生成器。It is a fast way to generate random numbers on demand that is portable between platforms for the same MySQL version.这是一种按需生成随机数的快速方法，可在同一MySQL版本的平台之间移植。

This function is unsafe for statement-based replication. 此函数对于基于语句的复制不安全。A warning is logged if you use this function when binlog_format is set to STATEMENT.如果在binlog_format设置为STATEMENT时使用此函数，则会记录警告。

ROUND(X), ROUND(X,D)

Rounds the argument X to D decimal places. 将参数X四舍五入到D个小数位。The rounding algorithm depends on the data type of X. 舍入算法取决于X的数据类型。D defaults to 0 if not specified. 如果未指定D，则它默认为0。D can be negative to cause D digits left of the decimal point of the value X to become zero. D可以是负数，使值X小数点左边的D位变为零。The maximum absolute value for D is 30; any digits in excess of 30 (or -30) are truncated.D的最大绝对值为30；任何超过30（或-30）的数字都将被截断。

mysql> SELECT ROUND(-1.23);
        -> -1
mysql> SELECT ROUND(-1.58);
        -> -2
mysql> SELECT ROUND(1.58);
        -> 2
mysql> SELECT ROUND(1.298, 1);
        -> 1.3
mysql> SELECT ROUND(1.298, 0);
        -> 1
mysql> SELECT ROUND(23.298, -1);
        -> 20
mysql> SELECT ROUND(.12345678901234567890123456789012345, 35);
        -> 0.123456789012345678901234567890

The return value has the same type as the first argument (assuming that it is integer, double, or decimal). 返回值的类型与第一个参数相同（假设它是整数、双精度或十进制）。This means that for an integer argument, the result is an integer (no decimal places):这意味着对于整数参数，结果是整数（无小数点）：

mysql> SELECT ROUND(150.000,2), ROUND(150,2);
+------------------+--------------+
| ROUND(150.000,2) | ROUND(150,2) |
+------------------+--------------+
|           150.00 |          150 |
+------------------+--------------+

ROUND() uses the following rules depending on the type of the first argument:ROUND()根据第一个参数的类型使用以下规则：

The following example shows how rounding differs for exact and approximate values:以下示例显示精确值和近似值的舍入差异：

mysql> SELECT ROUND(2.5), ROUND(25E-1);
+------------+--------------+
| ROUND(2.5) | ROUND(25E-1) |
+------------+--------------+
| 3          |            2 |
+------------+--------------+

For more information, see Section 12.25, “Precision Math”.有关更多信息，请参阅第12.25节，“精确数学”。

In MySQL 8.0.21 and later, the data type returned by ROUND() (and TRUNCATE()) is determined according to the rules listed here:在MySQL 8.0.21及更高版本中，ROUND()（和TRUNCATE()）返回的数据类型根据下面列出的规则确定：

SIGN(X)

Returns the sign of the argument as -1, 0, or 1, depending on whether X is negative, zero, or positive.根据X是负、零还是正，将参数的符号返回为-1、0或1。

mysql> SELECT SIGN(-32);
        -> -1
mysql> SELECT SIGN(0);
        -> 0
mysql> SELECT SIGN(234);
        -> 1

SIN(X)

Returns the sine of X, where X is given in radians.返回X的正弦，其中X以弧度表示。

mysql> SELECT SIN(PI());
        -> 1.2246063538224e-16
mysql> SELECT ROUND(SIN(PI()));
        -> 0

SQRT(X)

Returns the square root of a nonnegative number X.返回非负数X的平方根。

mysql> SELECT SQRT(4);
        -> 2
mysql> SELECT SQRT(20);
        -> 4.4721359549996
mysql> SELECT SQRT(-16);
        -> NULL

TAN(X)

Returns the tangent of X, where X is given in radians.返回X的正切值，其中X以弧度表示。

mysql> SELECT TAN(PI());
        -> -1.2246063538224e-16
mysql> SELECT TAN(PI()+1);
        -> 1.5574077246549

TRUNCATE(X,D)

Returns the number X, truncated to D decimal places. 返回数字X，截断为D个小数位。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。D can be negative to cause D digits left of the decimal point of the value X to become zero.D可以是负数，使值X小数点左边的D位变为零。

mysql> SELECT TRUNCATE(1.223,1);
        -> 1.2
mysql> SELECT TRUNCATE(1.999,1);
        -> 1.9
mysql> SELECT TRUNCATE(1.999,0);
        -> 1
mysql> SELECT TRUNCATE(-1.999,1);
        -> -1.9
mysql> SELECT TRUNCATE(122,-2);
       -> 100
mysql> SELECT TRUNCATE(10.28*100,0);
       -> 1028

All numbers are rounded toward zero.所有数字都向零舍入。

In MySQL 8.0.21 and later, the data type returned by TRUNCATE() follows the same rules that determine the return type of the ROUND() function; for details, see the description for ROUND().在MySQL 8.0.21及更高版本中，TRUNCATE()返回的数据类型遵循与ROUND()函数返回类型相同的规则；有关详细信息，请参见ROUND()的说明。