在从中获取数据的循环中更新游标的查询 table 是否合法

Question

例如，下面的操作可以吗？

DECLARE aId VARCHAR(20);
DECLARE cur1 CURSOR FOR SELECT  id FROM new_records WHERE is_loaded = false;
read_loop: LOOP

    FETCH cur1 INTO aId;
    ...
    update new_records set is_loaded = True where id = aId ; 
    ...
    CLOSE cur1;
END

Answer 1

MySQL 中的游标是 ASENSITIVE (13.6.6 Cursors)。

An INSENSITIVE Cursor is a Cursor that effectively causes a separate copy of its result Table to be created; the Cursor accesses that copy, rather than the original result, so any changes made to the original result by other methods won't be visible to this Cursor. A SENSITIVE Cursor is a Cursor that works directly on its result Table: it makes no copy, so other changes made to the result Table will be visible to this Cursor. An ASENSITIVE Cursor may or may not make a copy of its result Table; whether other changes to its result Table will be visible is implementation-defined. The default is an ASENSITIVE Cursor.

- 来自 DECLARE CURSOR Statement -

SQL Fiddle demo

但是，根据您需要执行的操作，还有其他方法可以更新 table。

在从中获取数据的循环中更新游标的查询 table 是否合法

Is it legal to update cursor's querying table in the loop of fetching data from it

mysql

stored-procedures

cursor