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MySQL 5.0 Reference Manual - Mathematical Functions

정보-기술/소프트웨어 2007. 12. 26. 12:29

MySQL 5.0 Reference Manual
Mathematical Functions

Name	Description
`ABS()`	Return the absolute value
`ACOS()`	Return the arc cosine
`ASIN()`	Return the arc sine
`ATAN2()`, `ATAN()`	Return the arc tangent of the two arguments
`ATAN()`	Return the arc tangent
`CEIL()`	Return the smallest integer value not less than the argument
`CEILING()`	Return the smallest integer value not less than the argument
`CONV()`	Convert numbers between different number bases
`COS()`	Return the cosine
`COT()`	Return the cotangent
`CRC32()`(v4.1.0)	Compute a cyclic redundancy check value
`DEGREES()`	Convert radians to degrees
`EXP()`	Raise to the power of
`FLOOR()`	Return the largest integer value not greater than the argument
`MOD()`	Return the remainder
`LN()`	Return the natural logarithm of the argument
`LOG10()`	Return the base-10 logarithm of the argument
`LOG2()`	Return the base-2 logarithm of the argument
`LOG()`	Return the natural logarithm of the first argument
`OCT()`	Return an octal representation of a decimal number
`PI()`	Return the value of pi
`POW()`	Return the argument raised to the specified power
`POWER()`	Return the argument raised to the specified power
`RADIANS()`	Return argument converted to radians
`RAND()`	Return a random floating-point value
`ROUND()`	Round the argument
`SIGN()`	Return the sign of the argument
`SIN()`	Return the sine of the argument
`SQRT()`	Return the square root of the argument
`TAN()`	Return the tangent of the argument
`TRUNCATE()`	Truncate to specified number of decimal places

All mathematical functions return NULL in the event of an error.

ABS(X)

Returns the absolute value of X.

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

This function is safe to use with BIGINT values.

ACOS(X)

Returns the arc cosine of X, that is, the value whose cosine is X. Returns NULL if X is not in the range -1 to 1.

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. Returns NULL if X is not in the range -1 to 1.

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.

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. 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.
```
mysql> SELECT ATAN(-2,2);
        -> -0.78539816339745
mysql> SELECT ATAN2(PI(),0);
        -> 1.5707963267949
```
CEIL(X)
CEIL() is a synonym for CEILING().
CEILING(X)
Returns the smallest integer value not less than X.
```
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. For string or floating-point arguments, the return value has a floating-point type.
CONV(N,from_base,to_base)
Converts numbers between different number bases. Returns a string representation of the number N, converted from base from_base to base to_base. Returns NULL if any argument is NULL. The argument N is interpreted as an integer, but may be specified as an integer or a string. The minimum base is 2 and the maximum base is 36. If to_base is a negative number, N is regarded as a signed number. Otherwise, N is treated as unsigned. CONV() works with 64-bit precision.
```
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'+0xa,10,10);
        -> '40'
```
COS(X)
Returns the cosine of X, where X is given in radians.
```
mysql> SELECT COS(PI());
        -> -1
```

COT(X)

Returns the cotangent of X.

mysql> SELECT COT(12);
        -> -1.5726734063977
mysql> SELECT COT(0);
        -> NULL

CRC32(expr)
Computes a cyclic redundancy check value and returns a 32-bit unsigned value. The result is NULL if the argument is NULL. The argument is expected to be a string and (if possible) is treated as one if it is not.
```
mysql> SELECT CRC32('MySQL');
        -> 3259397556
mysql> SELECT CRC32('mysql');
        -> 2501908538
```

DEGREES(X)

Returns the argument X, converted from radians to degrees.

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.

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.
```
mysql> SELECT FLOOR(1.23);
        -> 1
mysql> SELECT FLOOR(-1.23);
        -> -2
```
For exact-value numeric arguments, the return value has an exact-value numeric type. For string or floating-point arguments, the return value has a floating-point type.
FORMAT(X,D)
Formats the number X to a format like '#,###,###.##', rounded to D decimal places, and returns the result as a string. For details, see Section 10.4, “String Functions”.
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. See this function's description in Section 10.4, “String Functions”, for details.
LN(X)
Returns the natural logarithm of X; that is, the base-e logarithm of X.
```
mysql> SELECT LN(2);
        -> 0.69314718055995
mysql> SELECT LN(-2);
        -> NULL
```
This function is synonymous with LOG(X).
LOG(X), LOG(B,X)
If called with one parameter, this function returns the natural logarithm of X.
```
mysql> SELECT LOG(2);
        -> 0.69314718055995
mysql> SELECT LOG(-2);
        -> NULL
```
If called with two parameters, this function returns the logarithm of X for an arbitrary base B.
```
mysql> SELECT LOG(2,65536);
        -> 16
mysql> SELECT LOG(10,100);
        -> 2
```
LOG(B,X) is equivalent to LOG(X) / LOG(B).
LOG2(X)
Returns the base-2 logarithm of X.
```
mysql> SELECT LOG2(65536);
        -> 16
mysql> SELECT LOG2(-100);
        -> NULL
```
LOG2() is useful for finding out how many bits a number requires for storage. This function is equivalent to the expression LOG(X) / LOG(2).

LOG10(X)

Returns the base-10 logarithm of X.

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

LOG10(X) is equivalent to LOG(10,X).

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

Modulo operation. Returns the remainder of N divided by M.

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.

MOD() also works on values that have a fractional part and returns the exact remainder after division:

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

MOD(N,0) returns NULL.

PI()
Returns the value of π (pi). The default number of decimal places displayed is seven, but MySQL uses the full double-precision value internally.
```
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.

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

POWER(X,Y)
This is a synonym for POW().
RADIANS(X)
Returns the argument X, converted from degrees to radians. (Note that π radians equals 180 degrees.)
```
mysql> SELECT RADIANS(90);
        -> 1.5707963267949
```
RAND(), RAND(N)
Returns a random floating-point value v in the range 0 <= v < 1.0. If a constant integer argument N is specified, it is used as the seed value, which produces a repeatable sequence of column values.
```
mysql> SELECT RAND();
        -> 0.9233482386203
mysql> SELECT RAND(20);
        -> 0.15888261251047
mysql> SELECT RAND(20);
        -> 0.15888261251047
mysql> SELECT RAND();
        -> 0.63553050033332
mysql> SELECT RAND();
        -> 0.70100469486881
mysql> SELECT RAND(20);
        -> 0.15888261251047
```
The effect of using a non-constant argument is undefined. As of MySQL 5.0.13, non-constant arguments are disallowed.

To obtain a random integer R in the range i <= R < j, use the expression FLOOR(i + RAND() * (j – i)). For example, to obtain a random integer in the range the range 7 <= R < 12, you could use the following statement:
```
SELECT FLOOR(7 + (RAND() * 5));
```
You cannot use a column with RAND() values in an ORDER BY clause, because ORDER BY would evaluate the column multiple times. However, you can retrieve rows in random order like this:
```
mysql> SELECT * FROM tbl_name ORDER BY RAND();
```
ORDER BY RAND() combined with LIMIT is useful for selecting a random sample from a set of rows:
```
mysql> SELECT * FROM table1, table2 WHERE a=b AND c<d -> ORDER BY RAND() LIMIT 1000;
```
Note that RAND() in a WHERE clause is re-evaluated every time the WHERE is executed.

RAND() is not meant to be a perfect random generator, but instead is a fast way to generate ad hoc random numbers which is portable between platforms for the same MySQL version.
ROUND(X), ROUND(X,D)
Rounds the argument X to D decimal places. The rounding algorithm depends on the data type of X. D defaults to 0 if not specified. D can be negative to cause D digits left of the decimal point of the value X to become zero.
```
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
```
The return type is the same type as that of the first argument (assuming that it is integer, double, or decimal). This means that for an integer argument, the result is an integer (no decimal places):
```
mysql> SELECT ROUND(150.000,2), ROUND(150,2);
+------------------+--------------+
| ROUND(150.000,2) | ROUND(150,2) |
+------------------+--------------+
|           150.00 |          150 |
+------------------+--------------+
```
Before MySQL 5.0.3, the behavior of ROUND() when the argument is halfway between two integers depends on the C library implementation. Different implementations round to the nearest even number, always up, always down, or always toward zero. If you need one kind of rounding, you should use a well-defined function such as TRUNCATE() or FLOOR() instead.

As of MySQL 5.0.3, ROUND() uses the precision math library for exact-value arguments when the first argument is a decimal value:
- For exact-value numbers, ROUND() uses the “round half up” or “round toward nearest” rule: A value with a fractional part of .5 or greater is rounded up to the next integer if positive or down to the next integer if negative. (In other words, it is rounded away from zero.) A value with a fractional part less than .5 is rounded down to the next integer if positive or up to the next integer if negative.
- For approximate-value numbers, the result depends on the C library. On many systems, this means that ROUND() uses the "round to nearest even" rule: A value with any fractional part is rounded to the nearest even integer.
The following example shows how rounding differs for exact and approximate values:
```
mysql> SELECT ROUND(2.5), ROUND(25E-1);
+------------+--------------+
| ROUND(2.5) | ROUND(25E-1) |
+------------+--------------+
| 3          |            2 |
+------------+--------------+
```
For more information, see Chapter 21, Precision Math.

SIGN(X)

Returns the sign of the argument as -1, 0, or 1, depending on whether X is negative, zero, or positive.

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.

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

SQRT(X)

Returns the square root of a non-negative number X.

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.

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. If D is 0, the result has no decimal point or fractional part. D can be negative to cause D digits left of the decimal point of the value X to become zero.

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.

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