Question

这是我第一次使用游标上的MySQL，我遇到了一些问题，它不接受我的光标声明，我的代码有什么问题？它告诉我这个错误messgae：

#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中取出项目并将它们映射到最顶层声明的变量并执行你的语句。一旦它处理--Action to Loop Here部分中的语句，它就会通过从select语句中选择下一行来更改变量。这将重复，直到它处理选择中的所有行。

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

您尝试在一个语句中声明游标，然后在第二个语句中将查询与其关联。虽然有些数据库允许这样做，但我相当确定MySQL不是其中之一。此外，MySQL在声明所有变量之后才宣布游标是非常严格的。

这是我将如何做到的：

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;

MySQL声明游标错误

2 个答案: