Introduction to postgresql-- Mathematical function

1. Mathematical function

Mathematical functions are mainly used to deal with numerical data, the main mathematical functions are: absolute value function, trigonometric function (including sine function, tangent function, cotangent function, etc.), logarithmic function, random number function and so on. When an error occurs, the mathematical function returns a null value of null.

1.1.The absolute value function ABS (x) and the function PI () that returns pi

Example: find the absolute value of 2mai 3.3 mai 33

Testdb=# select abs (2), abs (- 3.3), abs (- 33)

Abs | abs | abs

-+-

2 | 3.3 | 33

(1 row)

Example: returns the value of pi, as follows:

Testdb=# select pi ()

Pi

-

3.14159265358979

(1 row)

1.2.The square root function sqrt (x) and the remainder function mod (x)

Sqrt (x) returns the quadratic square root of a non-negative number x

Mod (xPowery) returns the remainder of x divided by y. Mod () also works for values with decimal parts, returning the exact remainder after division.

Example: find the quadratic square root of 9 and 40:

Testdb=# select sqrt (9), sqrt (40)

Sqrt | sqrt

-+-

3 | 6.32455532033676

(1 row)

Note: a negative number does not have a square root. If the value evaluated is negative, an error message will be prompted.

Example: perform the remainder operation:

Testdb=# select mod (31), mod (234), mod (45.5)

Mod | mod | mod

-+-

7 | 4 | 3.5

(1 row)

1.3.Functions to get integers ceil (x), ceiling (x) and floor (x)

Ceil (x) and ceiling (x) have the same meaning, returning a minimum integer value of not less than x, and the return value is converted to a bigint.

Example: use the ceil and ceiling functions to return the smallest integer, as follows:

Testdb=# select ceil (- 3.35), ceiling (3.35)

Ceil | ceiling

-+-

-3 | 4

(1 row)

Example: use the floor function to return the maximum integer value, as follows

Testdb=# select floor (- 3.35), floor (3.35)

Floor | floor

-+-

-4 | 3

(1 row)

1.4.The rounding functions round (x) and round (x)

Round (x) returns the integer closest to the parameter x, rounding the x value.

Round returns the number closest to the parameter x, whose value is retained to y places after the decimal point, and if y is negative, the x value is retained to the left of the decimal place.

Example: use the round (x) function to round the operands, such as:

Testdb=# select round (1.15), round (- 1.68), round (1.15), round (1.68)

Round | round | round | round

-+-

-1 |-2 | 1 | 2

(1 row)

Example: round up operands using the round (xQuery y) function, as shown in

Testdb=# select round (1.38), round (1.38), round (231.36), round (231.36)

Round | round | round | round

-+-

1.4 | 1 | 230 | 200

(1 row)

1.5. symbolic function sign (x)

Sign (x) returns the symbol of the parameter. If the value of x is negative, zero or positive, the return result is:-1 zero 0 or 1.

Example:

Testdb=# select sign (- 21), sign (0), sign (21)

Sign | sign | sign

-+-

-1 | 0 | 1

(1 row)

1.6.The power operation functions pow (x ~ () ~ y), power (x ~ ()) and exp (x)

The function pow (xMagine y), power (xjingy) returns the result value of the y power of x.

Exp (x) returns the value of e to the power of x

Example: use the pow,power function for multiplier operations, such as:

Testdb=# select pow (2), power (2), pow (2), power (2)

Pow | power | pow | power

-+-

4 | 4 | 0.25 | 0.25

(1 row)

Example: use exp (x) to return the value of e to the power of x

Testdb=# select exp (3), exp (- 3), exp (0)

Exp | exp | exp

-+-

20.0855369231877 | 0.0497870683678639 | 1

(1 row)

1.7. logarithmic operation function: log (x)

Log (x) returns the natural number of x, the logarithm of x relative to the cardinality e. The logarithmic definition field cannot be negative, so an array of negative numbers will pop up an error message.

Testdb=# select log (3)

Log

-

0.477121254719662

(1 row)

1.8. the function of conversion between angle and Radian: radians (x) and degrees (x)

Radians (x) converts the parameter x from angles to radians.

Such as:

Testdb=# select radians 90, radians 180)

Radians | radians

-+-

1.5707963267949 | 3.14159265358979

(1 row)

Degrees (x) converts the parameter x from radians to angles, such as:

Testdb=# select degrees (pi ()), degrees (pi () / 2)

Degrees | degrees

-+-

180 | 90

(1 row)

1.9. sine function: sin (x) and Arcsine function: asin (x)

Sin (x) returns the sine of x, where x is the arc value.

Testdb=# select sin (1), round (sin (pi ()

Sin | round

-+-

0.841470984807897 | 0

(1 row)

Asin (x) returns the sine of x, that is, the value where the sine is x. If x is not in the range of-1 to 1, an error message pops up: input is out of range.

1.10. CoSine function: cos (x) and inverse cosine function: acos (x)

Cos (x) returns the cosine of x, where x is the arc value.

Testdb=# select cos (0), cos (pi ()), cos (1)

Cos | cos | cos

-+-

1 |-1 | 0.54030230586814

(1 row)

Acos (x) returns the inverse cosine of x, that is, the cosine is the value of x. If x is not in the range of-1 to 1, an error message will pop up.

Testdb=# select acos (1), acos (0), round (acos (0.54030230586814))

Acos | acos | round

-+-

0 | 1.5707963267949 | 1

(1 row)

Tangent function: tan (x), Arctangent function: atan (x), Cotangent function: cot (x)

Tan (x) returns the tangent of x, where x is the given arc value.

Example:

Testdb=# select tan, round (tan (pi () / 4))

Tan | round

-+-

0.309336249609623 | 1

(1 row)

Atan (x) returns the inverse tangent of x, that is, the value of the tangent to x.

Example:

Testdb=# select atan (0.309336249609623), atan (1)

Atan | atan

-+-

0.3 | 0.785398163397448

(1 row)

Cot (x) returns the cotangent of x.

Example:

Testdb=# select cot, 1/tan, cot (pi () / 4)

Cot |? column? | cot

-+-

3.23272814376583 | 3.23272814376583 | 1

(1 row)