我写了一个函数，如果我写了一个字符串，它会在输出中抛出字符。 但是我在最后的代码中显示了错误

Question

SET SERVEROUTPUT ON;

CREATE OR REPLACE FUNCTION string_to_char (
    c1 NUMBER,
    c2 VARCHAR2,
    c3 VARCHAR2
) RETURN VARCHAR2 IS

    c1 NUMBER := 1;
    c2 VARCHAR2(20);
    c3 VARCHAR2(20) := ( '&c3' );
BEGIN
    FOR c1 IN 1..20 LOOP
        SELECT
            substr(c3, c1, 1)
        INTO c2
        FROM
            dual;

        dbms_output.put_line(c2);
    END LOOP;
END;

/*
Function STRING_TO_CHAR compiled

LINE/COL  ERROR
--------- -------------------------------------------------------------
0/0       PL/SQL: Compilation unit analysis terminated
1/1       PLS-00410: duplicate fields in RECORD,TABLE or argument list are not permitted
Errors: check compiler log
*/

Answer 1

您用相同的名称命名了太多东西（在您的情况下为c1 ）：

• 函数参数
• 局部变量
• FOR循环中的计数器

如果您将其修改为例如

SQL> set serveroutput on
SQL>
SQL> CREATE OR REPLACE FUNCTION string_to_char (c1  NUMBER,
  2                                             c2  VARCHAR2,
  3                                             c3  VARCHAR2)
  4     RETURN VARCHAR2
  5  IS
  6     pc1  NUMBER := 1;
  7     pc2  VARCHAR2 (20);
  8     pc3  VARCHAR2 (20) := c3;
  9  BEGIN
 10     FOR i IN 1 .. 20
 11     LOOP
 12        SELECT SUBSTR (c3, c1, 1) INTO pc2 FROM DUAL;
 13
 14        DBMS_OUTPUT.put_line (pc2);
 15     END LOOP;
 16
 17     RETURN pc2;
 18  END;
 19  /

Function created.

SQL>

然后它编译并工作（虽然，我不确定我理解它的目的是什么）：

SQL> SELECT string_to_char (1, 'A', 'B') FROM DUAL;

STRING_TO_CHAR(1,'A','B')
--------------------------------------------------------------------------------
B

B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
SQL>