關係運算子比較兩個表示式或值，並返回一個布林結果。 下表顯示了PL/SQL支援的所有關係運算子。假設變數A=10，變數B=20，則 -
| 運算子 | 範例 | 範例 |
|---|---|---|
= |
檢查兩個運算元的值是否相等，如果是，則條件成立。 | (A = B)為假 |
!=,<>，~= |
檢查兩個運算元的值是否相等，如果兩個值不相等則條件成為真。 | (A != B)為真 |
> |
檢查左運算元的值是否大於右運算元的值，如果是，則條件成為真。 | (A > B) 為假 |
< |
檢查左運算元的值是否小於右運算元的值，如果是，則條件成為真。 | (A < B) 條件為真。 |
>= |
檢查左運算元的值是否大於或等於右運算元的值，如果是，則條件成為真。 | (A >= B) 為假 |
<= |
檢查左運算元的值是否小於或等於右運算元的值，如果是，則條件成為真。 | (A <= B) 為真 |
範例
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;
/
當上述程式碼在SQL提示下執行後，會產生以下結果 -
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