关系运算符 关系运算符比较两个表达式或值,并返回一个布尔结果。下表列出了所有PL/SQL支持的关系运算符。假设变量A=10,变量B=20,则: 运算符 | 描述 | 示例 | = | 检查两个操作数的值是否相等,如果是的话那么条件为真。 | (A = B) 结果为 false. | !=
<>
~= | 检查两个操作数的值是否相等,如果值不相等,则条件变为真。 | (A != B) 结果为 true. | > | 检查左边的操作数的值是否大于右操作数的值,如果是的话那么条件为真。 | (A > B) 结果为 false. | < | 检查左边的操作数的值是否小于右操作数的值,如果是的话那么条件为真。 | (A < B) 结果为 true. | >= | 检查左边的操作数的值是否大于或等于右操作数的值,如果是的话那么条件为真。 | (A >= B) 结果为 false. | <= | 检查左边的操作数的值是否小于或等于右操作数的值,如果是的话那么条件为真。 | (A <= B) 结果为 true. | 示例:DECLARE a number (2) := 21; b number (2) := 10;BEGIN IF (a = b) thendbms_output.put_line('Line 1 - a is equal to b'); ELSEdbms_output.put_line('Line 1 - a is not equal to b'); END IF; IF (a < b) thendbms_output.put_line('Line 2 - a is less than b'); ELSEdbms_output.put_line('Line 2 - a is not less than b'); END IF; IF ( a > b ) THENdbms_output.put_line('Line 3 - a is greater than b'); ELSEdbms_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 ) THENdbms_output.put_line('Line 4 - a is either equal or less than b'); END IF; IF ( b >= a ) THENdbms_output.put_line('Line 5 - b is either equal or greater than a'); END IF; IF ( a <> b ) THENdbms_output.put_line('Line 6 - a is not equal to b'); ELSEdbms_output.put_line('Line 6 - a is equal to b'); END IF;END;/当上述代码在SQL提示符执行时,它产生了以下结果:
Line 1 - a is not equal to bLine 2 - a is not less than bLine 3 - a is greater than bLine 4 - a is either equal or less than bLine 5 - b is either equal or greater than aLine 6 - a is not equal to bPL/SQL procedure successfully completed
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