调用“||”时的参数数量或类型错误

我们应该读取一个文本文件，在处理异常的同时将该数据插入到表中。这是我的函数的代码：

set serveroutput ON; 
CREATE OR replace FUNCTION Order_func(ldir  VARCHAR2, 
                                      lfile VARCHAR2) 
RETURN BOOLEAN 
AS 
  result       BOOLEAN; 
  f            utl_file.file_type; 
  s            VARCHAR2(200); 
  v_row        VARCHAR2(2000); 
  v1           NUMBER; 
  v2           NUMBER; 
  v3           NUMBER; 
  v4           DATE; 
  v5           DATE; 
  v6           NUMBER; 
  v7           NUMBER; 
  v8           NUMBER; 
  v9           NUMBER; 
  customer_error EXCEPTION; 
  employee_error EXCEPTION; 
  item_error EXCEPTION; 
  customerids  NUMBER; 
  employeeids  NUMBER; 
  inventoryids NUMBER; 
BEGIN 
    SELECT cno 
    INTO   customerids 
    FROM   customers; 

    SELECT employeeno 
    INTO   employeeids 
    FROM   employees; 

    SELECT itemno 
    INTO   inventoryids 
    FROM   inventory; 

    f := utl_file.Fopen(ldir, lfile, 'R'); 

    LOOP 
        utl_file.Get_line(f, v_row); 
        v1 := Substr(v_row, 1, 4); 
        v2 := Substr(v_row, 6, 9); 
        v3 := Substr(v_row, 11, 12); 
        v4 := Substr(v_row, 15, 23); 
        v5 := Substr(v_row, 27, 35); 
        v6 := Substr(v_row, 38, 41); 
        v7 := Substr(v_row, 43); 
        v8 := Substr(v_row, 45, 48); 
        v9 := Substr(v_row, 50, 51); 
        IF v2 <> customerids THEN --checking customer id 
          RAISE customer_error; 
        ELSIF v3 <> employeeids THEN --checking employee id 
          RAISE employee_error; 
        ELSIF v6 <> inventoryids THEN --checking item1 id 
          RAISE item_error; 
        ELSIF v8 <> inventoryids THEN --checking item2 id 
          RAISE item_error; 
        ELSE 
          INSERT INTO transactions 
                      (tid, orderno,  cno,  employeeno,  received, 
                       shipped,  itemno1,  quantity1,  itemno2,  quantity2) 
          VALUES      (sequence_tid.NEXTVAL,  v1,  v2,  v3,  v4,  v5, 
                       v6,  v7,  v8,  v9); 
        END IF; 
    END LOOP; 

    result := TRUE; 

    RETURN result; 
EXCEPTION 
  WHEN customer_error THEN 
dbms_output.Put_line('Customer not found in parent Customer table'); WHEN 
employee_error THEN 
dbms_output.Put_line('Employee not found in Employee table'); 
                     WHEN item_error THEN 
dbms_output.Put_line('Item not found in inventory table'); WHEN OTHERS THEN 
dbms_output.Put_line('Error code:' 
                     || SQLCODE 
                     || '. Error Message: ' 
                     || SQLERRM); 

utl_file.Fclose(f); 

result := FALSE; 

RETURN result; 
END order_func; 

这就是我调用函数的方式（但我认为这是错误的）：

DECLARE
    results boolean;
BEGIN
    results := order_func('forQues','items.txt');
    DBMS_OUTPUT.PUT_LINE('Result for ORDER_FUNC Function is: ' || results);
END;

这是我遇到的错误：

DECLARE
    results boolean;
BEGIN
    results := order_func('forQues','items.txt');
    DBMS_OUTPUT.PUT_LINE('Result for ORDER_FUNC Function is: ' || results);
END;
Error report -
ORA-06550: line 5, column 26:
PLS-00306: wrong number or types of arguments in call to '||'
ORA-06550: line 5, column 5:
PL/SQL: Statement ignored
06550. 00000 -  "line %s, column %s:\n%s"
*Cause:    Usually a PL/SQL compilation error.
*Action:

我试图删除 dbms_output 中的结果，这就是发生的事情：

DECLARE
    results boolean;
BEGIN
    results := order_func('forQues','items.txt');
    DBMS_OUTPUT.PUT_LINE('Result for ORDER_FUNC Function is:');
END;

运行后我得到：

Error code:-1422. Error Message: ORA-01422: exact fetch returns more than requested number of rows
Result for ORDER_FUNC Function is:


PL/SQL procedure successfully completed.

请有人帮忙，如何解决这个问题？