Plsql 简明教程
PL/SQL - Operators
在本章中，我们将讨论 PL/SQL 中的操作符。操作符是一个符号，告诉编译器执行特定的数学或逻辑操作。PL/SQL 语言中内置了丰富的操作符，并提供了以下类型的操作符 −
In this chapter, we will discuss operators in PL/SQL. An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulation. PL/SQL language is rich in built-in operators and provides the following types of operators −
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Arithmetic operators
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Relational operators
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Comparison operators
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Logical operators
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String operators
在这里，我们将逐个了解算术、关系、比较和逻辑操作符。字符串操作符将在本章节后面讨论 − PL/SQL - Strings 。
Here, we will understand the arithmetic, relational, comparison and logical operators one by one. The String operators will be discussed in a later chapter − PL/SQL - Strings.
Arithmetic Operators
以下表格显示了 PL/SQL 支持的所有算术运算符。我们假设 variable A 含 10， variable B 含 5，则 −
Following table shows all the arithmetic operators supported by PL/SQL. Let us assume variable A holds 10 and variable B holds 5, then −
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 |
Relational Operators
关系运算符比较两个表达式或值并返回布尔结果。以下表格显示了 PL/SQL 支持的所有关系运算符。我们假设 variable A 含 10， variable B 含 20，则 −
Relational operators compare two expressions or values and return a Boolean result. Following table shows all the relational operators supported by PL/SQL. Let us assume variable A holds 10 and variable B holds 20, then −
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 |
Comparison Operators
比较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 。
Comparison operators are used for comparing one expression to another. The result is always either TRUE, FALSE or NULL.
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. |
Logical Operators
下表显示 PL/SQL 支持的逻辑运算符。所有这些运算符都针对布尔操作数工作，并产生布尔结果。让我们假设 variable A 为真， variable B 为假，那么 −
Following table shows the Logical operators supported by PL/SQL. All these operators work on Boolean operands and produce Boolean results. Let us assume variable A holds true and variable B holds false, then −
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 Operator Precedence
运算符优先级确定表达式中项的分组。这会影响表达式的求值方式。某些运算符比其他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。
Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator.
例如， x = 7 + 3 * 2 ；在这里， x 被赋值为 13 ，而不是 20，因为运算符 * 的优先级高于 +，因此它首先与 3*2 相乘，然后再加到 7 中。
For example, x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.
此处，优先级最高的运算符显示在表顶部，优先级最低的运算符显示在表底部。在表达式中，将首先评估优先级较高的运算符。
Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.
运算符的优先级如下：=、<、>、⇐、>=、<>、!=、~=、^=、IS NULL、LIKE、BETWEEN、IN。
The precedence of operators goes as follows: =, <, >, ⇐, >=, <>, !=, ~=, ^=, IS NULL, LIKE, BETWEEN, IN.
Operator |
Operation |
** |
exponentiation |
+, - |
identity, negation |
*, / |
multiplication, division |
+, -, |
|
addition, subtraction, concatenation |
|
comparison |
|
NOT |
logical negation |
AND |
conjunction |
OR |
inclusion |