Postgresql 简明教程

PostgreSQL - Operators

What is an Operator in PostgreSQL?

运算符是保留字或主要用于 PostgreSQL 语句的 WHERE 子句中的字符，用于执行运算（例如，比较和数学运算）。

An operator is a reserved word or a character used primarily in a PostgreSQL statement’s WHERE clause to perform operation(s), such as comparisons and arithmetic operations.

运算符用于指定 PostgreSQL 语句中的条件，并作为语句中多个条件的合取。

Operators are used to specify conditions in a PostgreSQL statement and to serve as conjunctions for multiple conditions in a statement.

Arithmetic operators
Comparison operators
Logical operators
Bitwise operators

PostgreSQL Arithmetic Operators

假设变量 a 存储 2，变量 b 存储 3，那么 −

Assume variable a holds 2 and variable b holds 3, then −

Example

Operator

Description

Example

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 Comparison Operators

假设变量 a 等于 10，变量 b 等于 20，则 −

Assume variable a holds 10 and variable b holds 20, then −

Show Examples

Operator

Description

Example

Checks if the values of two operands are equal or not, if yes then condition becomes true.

(a = b) is not true.

Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.

(a != b) is true.

Checks if the values 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 Logical Operators

以下是 PostgresSQL 中所有可用的逻辑运算符列表。

Here is a list of all the logical operators available in PostgresSQL.

Show Examples

S. No.

Operator & Description

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 Bit String Operators

按位运算符处理位，并执行逐位运算。& 和 | 的真值表如下 −

Bitwise operator works on bits and performs bit-by-bit operation. The truth table for & and | is as follows −

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

假设如果 A = 60；并且 B = 13；现在以二进制格式，它们将如下所示 −

Assume if A = 60; and B = 13; now in binary format they will be as follows −

A = 0011 1100

B = 0000 1101

A&B = 0000 1100

A|B = 0011 1101

~A  = 1100 0011

link:../postgresql/postgresql_bitwise-operators.html[Show Examples]

The Bitwise operators supported by PostgreSQL are listed in the following table −
[%autowidth]
|===

|Operator|Description|Example
|&|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 -61 which is 1100 0011 in 2's complement form due to a signed binary number.
|<<|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 00110001
|===