在 MySQL 中声明游标时出现错误代码 #1064

Question

这是我第一次在 MySQL 上使用游标，我遇到了一些问题，它不接受我的游标声明，我的代码有什么问题？它向我显示此错误消息：

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DECLARE @MyCursor CURSOR' at line 1

我的代码是：

DECLARE @MyCursor CURSOR;
DECLARE @MyField varchar2(255);

BEGIN
    SET @MyCursor = CURSOR FOR
    SELECT codeMaint from affectationmc where iduser=29;     

    OPEN @MyCursor 
        FETCH NEXT FROM @MyCursor 
        INTO @MyField

        WHILE @@FETCH_STATUS = 0
        BEGIN
          delete from mcorr where codemaint=@MyField ;
          FETCH NEXT FROM @MyCursor 
          INTO @MyField 
        END; 

    CLOSE @MyCursor ;

    DEALLOCATE @MyCursor;
END;

Answer 1

这是我用于游标的模板。它只是从 select 中获取项目并将它们映射到顶部声明的变量并执行您的语句。一旦它处理了 --Actions to Loop Here 部分中的语句，它就会通过 selecting 您的 select 语句的下一行来更改变量。重复此操作，直到它处理 select.

中的所有行

DECLARE 

 @variable_A AS varchar(15)
,@variable_B AS INT
,@variable_C AS INT
,@variable_D AS VARCHAR(255)

DECLARE Process_Name CURSOR LOCAL FAST_FORWARD FOR 
            SELECT 
                        T.Col_A,T.Col_B,T.Col_C,T.Col_D
            FROM 
                        tab.my_table AS T;


OPEN Process_Name 
FETCH NEXT FROM Process_Name INTO @variable_A,@variable_B,@variable_C,@variable_D

WHILE @@FETCH_STATUS = 0
BEGIN


--Actions to Loop Here


FETCH NEXT FROM Process_Name INTO @variable_A,@variable_B,@variable_C,@variable_D
END

CLOSE Process_Name 
DEALLOCATE Process_Name

Answer 2

您试图在一个语句中声明游标，然后在第二个语句中将查询与其相关联。虽然有些数据库允许这样做，但我很确定 MySQL 不是其中之一。此外，MySQL 非常严格，直到在声明所有变量之后才声明游标。

以下是我的做法：

BEGIN  -- note all declarations are inside the BEGIN/END
  DECLARE done INT DEFAULT FALSE;  -- Good practice is to avoid global variables whenever possible
  DECLARE MyField varchar(255); -- varchar2 is Oracle, not MySQL

  DECLARE MyCursor CURSOR FOR
    SELECT codeMaint
      FROM affectationmc
      WHERE iduser = 29;

  DECLARE CONTINUE HANDLER FOR NOT FOUND
    SET done = TRUE;  -- this will detect end-of-result-set

  OPEN MyCursor;
  read_loop: LOOP
    FETCH NEXT
      FROM MyCursor 
      INTO MyField;
    IF done THEN
      LEAVE read_loop;
    END IF;

    DELETE FROM mcorr
      WHERE codemaint = MyField ;
  END LOOP;

  CLOSE MyCursor;
END;

在 MySQL 中声明游标时出现错误代码 #1064

error code #1064 while Declaring Cursor in MySQL

mysql

cursor