一、注释分为单行注释和多行注释两种。

    1.单行注释使用“--”。

        DECLARE

        howmany NUMBER;

        num_tables NUMBER;

        BEGIN

        -- Begin processing

        SELECT COUNT(*) INTO howmany

        FROM USER_OBJECTS

        WHERE OBJECT_TYPE = 'TABLE';     -- Check number of tables

        num_tables := howmany; -- Compute another value

        END;

    2.多行注释以“/*”开始,“*/”结尾。

        DECLARE

        some_condition BOOLEAN;

        pi NUMBER := 3.1415926;

        radius NUMBER := 15;

        area NUMBER;

        BEGIN

        /* Perform some simple tests and assignments */

        IF 2 + 2 = 4 THEN

        some_condition := TRUE;

        /* We expect this THEN to always be performed */

        END IF;

        /* This line computes the area of a circle using pi,

        which is the ratio between the circumference and diameter.

        After the area is computed, the result is displayed. */

        area := pi * radius**2;

        DBMS_OUTPUT.PUT_LINE('The area is: ' || TO_CHAR(area));

        END;

二、使用注释需要注意点

    1.多行注释不能进行嵌套，如下面是错误的：

         /*

        IF 2 + 2 = 4 THEN

        some_condition := TRUE;

        /* We expect this THEN to always be performed */

        END IF;

        */

    2.多行注释里面可以嵌套单行注释：

        /*

        IF 2 + 2 = 4 THEN

        some_condition := TRUE;

        -- We expect this THEN to always be performed

        END IF;

        */