什麼是PostgreSQL運算符?
運算符是一個保留字或字符主要用於PostgreSQL的語句的WHERE子句中執行操作，如比較和算術運算。
運算符用於指定一個PostgreSQL表中的條件，並在一份聲明中多個條件作為連詞。
PostgreSQL算術運算符：
假設變量a的值為2，而變量b的值為3：
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運算符 |
描述 |
實例 |
+
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比較運算符:
假設變量，a變量的值為10，變量b的值為20:
查看實例
運算符 |
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邏輯運算符：
這裡是一個所有的邏輯運算符可以在PostgreSQL中使用的列表。
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運算符 |
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：
位運算符位和位操作執行位。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
假設如果A= 60，B =13，他們現在以二進制格式將如下：
A = 0011 1100
B = 0000 1101
-----------------
A&B = 0000 1100
A|B = 0011 1101
~A = 1100 0011
PostgreSQL支持位運算符下表中列出。假設變量A=60和變量B=13，那麼：
查看實例
運算符 |
描述 |
實例 |
&
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
