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📜  PL / SQL-运算符

📅  最后修改于: 2020-11-26 05:51:48             🧑  作者: Mango

在本章中，我们将讨论PL / SQL中的运算符。运算符是告诉编译器执行特定数学或逻辑运算的符号。 PL / SQL语言具有丰富的内置运算符，并提供以下类型的运算符-

  • 算术运算运算符
  • 关系运算符
  • 运算符
  • 逻辑运算符
  • 字符串运算符

在这里，我们将一一理解算术，关系，比较和逻辑运算符。字符串运算符将在后面的章节-PL / SQL-Strings中讨论。

算术运算符

下表显示了PL / SQL支持的所有算术运算运算符。假设变量A持有10，变量B持有5，则-

显示范例

Operator Description Example
+ Adds two operands A + B will give 15
– Subtracts second operand from the first A – B will give 5
* Multiplies both operands A * B will give 50
/ Divides numerator by de-numerator A / B will give 2
** Exponentiation operator, raises one operand to the power of other A ** B will give 100000

关系运算符

关系运算符比较两个表达式或值，并返回布尔结果。下表显示了PL / SQL支持的所有关系运算符。让我们假设变量A持有10，变量B持有20，那么-

显示范例

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 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

比较运算符

运算符用于将一个表达式与另一个表达式进行比较。结果始终为TRUE，FALSE或NULL 。

显示范例

Operator Description Example
LIKE The LIKE operator compares a character, string, or CLOB value to a pattern and returns TRUE if the value matches the pattern and FALSE if it does not. If ‘Zara Ali’ like ‘Z% A_i’ returns a Boolean true, whereas, ‘Nuha Ali’ like ‘Z% A_i’ returns a Boolean false.
BETWEEN The BETWEEN operator tests whether a value lies in a specified range. x BETWEEN a AND b means that x >= a and x <= b. If x = 10 then, x between 5 and 20 returns true, x between 5 and 10 returns true, but x between 11 and 20 returns false.
IN The IN operator tests set membership. x IN (set) means that x is equal to any member of set. If x = ‘m’ then, x in (‘a’, ‘b’, ‘c’) returns Boolean false but x in (‘m’, ‘n’, ‘o’) returns Boolean true.
IS NULL The IS NULL operator returns the BOOLEAN value TRUE if its operand is NULL or FALSE if it is not NULL. Comparisons involving NULL values always yield NULL. If x = ‘m’, then ‘x is null’ returns Boolean false.

逻辑运算符

下表显示了PL / SQL支持的逻辑运算符。所有这些运算符都对布尔操作数起作用并产生布尔结果。让我们假设变量A成立，变量B成立，然后-

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Operator Description Examples
and Called the logical AND operator. If both the operands are true then condition becomes true. (A and B) is false.
or Called the logical OR Operator. If any of the two operands is true then condition becomes true. (A or B) is true.
not Called the logical NOT Operator. Used to reverse the logical state of its operand. If a condition is true then Logical NOT operator will make it false. not (A and B) is true.

PL / SQL运算符优先级

运算符优先级确定表达式中术语的分组。这会影响表达式的求值方式。某些运算符具有更高的优先级；例如，乘法运算符的优先级高于加法运算符。

例如， x = 7 + 3 * 2 ;在这里， x被赋值为13而不是20，因为运算符*的优先级比+高，因此它首先与3 * 2相乘，然后加到7中。

在此，优先级最高的运算符出现在表格的顶部，而优先级最低的运算符出现在表格的底部。在表达式中，优先级较高的运算符将首先被评估。

运算符的优先级如下：=，<，>，<=，> =，<>，！=，〜=，^ =，IS NULL，LIKE，BETWEEN，IN。

显示范例

Operator Operation
** exponentiation
+, – identity, negation
*, / multiplication, division
+, -, || addition, subtraction, concatenation
comparison
NOT logical negation
AND conjunction
OR inclusion