Question

我想编写一个过程来检查表中列中是否存在特定的输入值。如果值确实存在，则输出错误消息，否则插入新行。

例如，这是所需的逻辑

CREATE OR REPLACE PROCEDURE class_day (p_class_day IN varchar2)
AS
  classday varchar2;
BEGIN

    IF ( SELECT class_Day INTO classday
           FROM tutprac
          WHERE classday = p_class_day) THEN

            dbms_output.put_line('do not allow insert');
    ELSE
      dbms_output.put_line('allow insert');
    END IF;
END;

Answer 1

您可以尝试这样的事情：

CREATE OR REPLACE PROCEDURE class_day (p_class_day IN varchar2) 
AS
 classday tutprac.class_Day%TYPE;
BEGIN
   SELECT class_Day 
     INTO classday
     FROM tutprac
    WHERE classday = p_class_day;

   -- If you get here, the record has been selected, therefore it already exists
   dbms_output.put_line('do not allow insert');
EXCEPTION
   WHEN no_data_found
   THEN
      -- The record did not exist, create it!
      dbms_output.put_line('allow insert');
   WHEN others
   THEN
      -- An unexpected error has occurred, report it!
      dbms_output.put_line(sqlerrm);
      RAISE;

END class_day;

Answer 2

为了避免使用捕获异常等的仪式，我们只需计算给定值出现的行。然后使用行数作为表中存在的值的标志。

CREATE OR REPLACE PROCEDURE class_day (p_class_day IN varchar2) 
AS
  l_count NUMBER;
BEGIN
   SELECT count(*)
     INTO l_count
     FROM tutprac
    WHERE classday = p_class_day
      AND rownum = 1; -- this line makes the query execution a little bit faster
                      -- and later we can remove it if we need exact amount of rows

   -- coming at this line
   -- we have fetched `l_count` value is either 0 or 1
   -- and guaranteed to avoid NO_DATA_FOUND and TOO_MANY_ROWS exceptions

   IF l_count = 0 THEN 
     -- value `p_class_day` is not found
     dbms_output.put_line('do not allow insert');
   ELSE
     -- at least one `p_class_day` is found
     dbms_output.put_line('allow insert');
   END IF;

END class_day;

Oracle sql存储过程检查表中是否已存在输入（如果未插入）

2 个答案: