这篇文章主要介绍“数据库CLOB为空的判断方法是什么”，在日常操作中，相信很多人在数据库CLOB为空的判断方法是什么问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”数据库CLOB为空的判断方法是什么”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
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下列的哪些选项在执行之后会显示 "CLOB has a length of 0" ?
(A)
DECLARE
l_clob CLOB;
BEGIN
IF l_clob IS NULL
THEN
DBMS_OUTPUT.put_line ('CLOB is NULL');
ELSE
DBMS_OUTPUT.put_line ('CLOB has a length of '
|| LENGTH (l_clob));
END IF;
END;
/SQL> DECLARE
2 l_clob CLOB;
3 BEGIN
4 IF l_clob IS NULL
5 THEN
6 DBMS_OUTPUT.put_line ('CLOB is NULL');
7 ELSE
8 DBMS_OUTPUT.put_line ('CLOB has a length of '
9 || LENGTH (l_clob));
10 END IF;
11 END;
12 /
CLOB is NULL
PL/SQL procedure successfully completed
SQL>(B)
DECLARE
l_clob CLOB := EMPTY_CLOB ();
BEGIN
IF l_clob IS NULL
THEN
DBMS_OUTPUT.put_line ('CLOB is NULL');
ELSE
DBMS_OUTPUT.put_line ('CLOB has a length of '
|| LENGTH (l_clob));
END IF;
END;
/SQL> DECLARE
2 l_clob CLOB := EMPTY_CLOB ();
3 BEGIN
4 IF l_clob IS NULL
5 THEN
6 DBMS_OUTPUT.put_line ('CLOB is NULL');
7 ELSE
8 DBMS_OUTPUT.put_line ('CLOB has a length of '
9 || LENGTH (l_clob));
10 END IF;
11 END;
12 /
CLOB has a length of 0
PL/SQL procedure successfully completed
SQL>(C)
DECLARE
l_clob CLOB := '';
BEGIN
IF l_clob IS NULL
THEN
DBMS_OUTPUT.put_line ('CLOB is NULL');
ELSE
DBMS_OUTPUT.put_line ('CLOB has a length of '
|| LENGTH (l_clob));
END IF;
END;
/SQL> DECLARE
2 l_clob CLOB := '';
3 BEGIN
4 IF l_clob IS NULL
5 THEN
6 DBMS_OUTPUT.put_line ('CLOB is NULL');
7 ELSE
8 DBMS_OUTPUT.put_line ('CLOB has a length of '
9 || LENGTH (l_clob));
10 END IF;
11 END;
12 /
CLOB is NULL
PL/SQL procedure successfully completed
SQL>(D)
DECLARE
l_clob1 CLOB := EMPTY_CLOB ();
l_clob2 CLOB := l_clob1;
BEGIN
IF l_clob2 IS NULL
THEN
DBMS_OUTPUT.put_line ('CLOB is NULL');
ELSE
DBMS_OUTPUT.put_line ('CLOB has a length of '
|| LENGTH (l_clob2));
END IF;
END;
/SQL> DECLARE
2 l_clob1 CLOB := EMPTY_CLOB ();
3 l_clob2 CLOB := l_clob1;
4 BEGIN
5 IF l_clob2 IS NULL
6 THEN
7 DBMS_OUTPUT.put_line ('CLOB is NULL');
8 ELSE
9 DBMS_OUTPUT.put_line ('CLOB has a length of '
10 || LENGTH (l_clob2));
11 END IF;
12 END;
13 /
CLOB has a length of 0
PL/SQL procedure successfully completed答案BD. 注意答案C里面的 '' 相当于NULL.
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