PL/SQL - 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 variable A 持有 10 而 variable B 持有 20，然后 −
| 运算符 | 描述 | 示例 |
|---|---|---|
| = | 检查两个操作数的值是否相等，如果是则条件为真。 | (A = B) is not true. |
!= <> ~= |
检查两个操作数的值是否相等，如果值不相等则条件为真。 | (A != B) is true. |
| > | 检查左操作数的值是否大于右操作数的值，如果是，则条件为真。 | (A > B) is not true. |
| < | 检查左操作数的值是否小于右操作数的值，如果是则条件为真。 | (A < B) is true. |
| >= | 检查左操作数的值是否大于或等于右操作数的值，如果是则条件为真。 | (A >= B) is not true. | <= | 检查左操作数的值是否小于或等于右操作数的值，如果是则条件为真。 | (A <= B) is true |
示例
DECLARE
a number (2) := 21;
b number (2) := 10;
BEGIN
IF (a = b) then
dbms_output.put_line('Line 1 - a is equal to b');
ELSE
dbms_output.put_line('Line 1 - a is not equal to b');
END IF;
IF (a < b) then
dbms_output.put_line('Line 2 - a is less than b');
ELSE
dbms_output.put_line('Line 2 - a is not less than b');
END IF;
IF ( a > b ) THEN
dbms_output.put_line('Line 3 - a is greater than b');
ELSE
dbms_output.put_line('Line 3 - a is not greater than b');
END IF;
-- Lets change value of a and b
a := 5;
b := 20;
IF ( a <= b ) THEN
dbms_output.put_line('Line 4 - a is either equal or less than b');
END IF;
IF ( b >= a ) THEN
dbms_output.put_line('Line 5 - b is either equal or greater than a');
END IF;
IF ( a <> b ) THEN
dbms_output.put_line('Line 6 - a is not equal to b');
ELSE
dbms_output.put_line('Line 6 - a is equal to b');
END IF;
END;
/
在 SQL 提示符下执行上述代码时，会产生以下结果 −
Line 1 - a is not equal to b Line 2 - a is not less than b Line 3 - a is greater than b Line 4 - a is either equal or less than b Line 5 - b is either equal or greater than a Line 6 - a is not equal to b PL/SQL procedure successfully completed
