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PostgreSQL运算符

什么是PostgreSQL运算符?

运算符是一个保留字或字符主要用于PostgreSQL的语句的WHERE子句中执行操作,如比较和算术运算。

运算符用于指定一个PostgreSQL表中的条件,并在一份声明中多个条件作为连词。

  • 算术运算符

  • 比较操作符

  • 逻辑运算符

  • 位运算符

PostgreSQL算术运算符:

假设变量a的值为2,而变量b的值为3:

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运算符 描述 实例
+ Addition - Adds values on either side of the operator a + b will give 5
- Subtraction - Subtracts right hand operand from left hand operand a - b will give -1
* Multiplication - Multiplies values on either side of the operator a * b will give 6
/ Division - Divides left hand operand by right hand operand b / a will give 1
% Modulus - Divides left hand operand by right hand operand and returns remainder b % a will give 1
^ Exponentiation - This gives the exponent value of the right hand operand a ^ b will give 8
|/ square root |/ 25.0 will give 5
||/ Cube root ||/ 27.0 will give 3
!/ factorial 5 ! will give 120
!! factorial (prefix operator) !! 5 will give 120

PostgreSQL比较运算符:

假设变量,a变量的值为10,变量b的值为20:

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运算符 描述 例子
= Checks if the value of two operands are equal or not, if yes then condition becomes true. (a = b) is not true.
!= Checks if the value of two operands are equal or not, if values are not equal then condition becomes true. (a != b) is true.
<> Checks if the value of two operands are equal or not, if values are not equal then condition becomes true. (a <> b) is true.
> Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. (a > b) is not true.
< Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. (a < b) is true.
>= Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. (a >= b) is not true.
<= Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. (a <= b) is true.

PostgreSQL逻辑运算符:

这里是一个所有的逻辑运算符可以在PostgreSQL中使用的列表。

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运算符 描述
AND The AND operator allows the existence of multiple conditions in a PostgresSQL statement's WHERE clause.
NOT The NOT operator reverses the meaning of the logical operator with which it is used. Eg. NOT EXISTS, NOT BETWEEN, NOT IN etc. This is negate operator.
OR The OR operator is used to combine multiple conditions in a PostgresSQL statement's WHERE clause.

PostgreSQL的位串操作符:

位运算符位和位操作执行位。真值表&|如下:

p q p & q p | q
0 0 0 0
0 1 0 1
1 1 1 1
1 0 0 1

假设如果A= 60,B =13,他们现在以二进制格式将如下:

A = 0011 1100

B = 0000 1101

-----------------

A&B = 0000 1100

A|B = 0011 1101

~A  = 1100 0011

PostgreSQL支持位运算符下表中列出。假设变量A=60和变量B=13,那么:

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运算符 描述 实例
& Binary AND Operator copies a bit to the result if it exists in both operands. (A & B) will give 12 which is 0000 1100
| Binary OR Operator copies a bit if it exists in either operand. (A | B) will give 61 which is 0011 1101
~ Binary Ones Complement Operator is unary and has the effect of 'flipping' bits. (~A ) will give -60 which is 1100 0011
<< Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand. A << 2 will give 240 which is 1111 0000
>> Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand. A >> 2 will give 15 which is 0000 1111
# bitwise XOR. A # B will give 49 which is 0100 1001