sql-如果不存在则插入

Question

我在使用SQL查询时遇到问题。如果同一行尚不存在，我需要插入一行。这是我到目前为止的内容：

DECLARE
BEGIN
   FOR FOLDER_ROW IN (SELECT FOLDERID, USERID FROM DATA1.FOLDERS)
      LOOP                       
          IF NOT EXISTS (SELECT * FROM DATA1.FOLDER_USER WHERE FOLDER_ID = FOLDER_ROW.FOLDERID AND USER_ID = FOLDER_ROW.USERID) 
          INSERT INTO DATA1.FOLDER_USER (FOLDER_ID, USER_ID) VALUES (FOLDER_ROW.FOLDERID, FOLDER_ROW.USERID);
     END LOOP;
    COMMIT;
END;

我对sql不太熟悉，尤其是不存在的语法，因此在执行时会出现以下错误：

ORA-06550：第37行，第11列：PLS-00103：在预期以下情况之一时遇到了符号“ INSERT”：

然后和或

用“ then”符号代替“ INSERT”继续。

ORA-06550: line 38, column 10:
PLS-00103: Encountered the symbol "LOOP" when expecting one of the

following:

   if
ORA-06550: line 40, column 5:
PLS-00103: Encountered the symbol "end-of-file" when expecting one of

the following:

   end not pragma final instantiable order overriding static
   member constructor map

Answer 1

在SQL中完成所有操作，而不是将上下文切换到PL / SQL：

INSERT INTO DATA1.FOLDERS
(folder_id,
 user_id)
SELECT f1.folder_id,
       f1.user_id
  FROM DATA1.FOLDERS f1
 WHERE NOT EXISTS (SELECT 1
                     FROM DATA1.FOLDERS f2
                    WHERE f1.folder_id = f2.folder_id
                      AND f1.user_id = f2.user_id);