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。
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算术运算符
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比较操作符
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逻辑运算符
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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：
| 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:
| 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。
| 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：
| 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 |
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欢迎任何形式的转载，但请务必注明出处，尊重他人劳动共创优秀实例教程
转载请注明：文章转载自：代码驿站 [http:/www.codeinn.net]
本文标题：PostgreSQL运算符
本文地址：http://www.codeinn.net/postgresql/936.html
