我已将我的问题简化为这个简单的 SP。列名最后被缓存在 SELECT * 中。我不知道为什么或如何阻止它。我尝试添加 SQL_NO_CACHE 但这没有什么区别。
DROP TABLE IF EXISTS foo;
CREATE TABLE foo(
col1 int,
col2 int);
INSERT INTO foo VALUES(1,2),(3,4),(5,6);
DROP PROCEDURE IF EXISTS mysp;
DELIMITER ;;
CREATE DEFINER=root@localhost PROCEDURE mysp(c INT)
BEGIN
DROP TABLE IF EXISTS mydata;
SET @mycol='col1';
IF c > 0 THEN SET @mycol:='col2';
END IF;
SET @s=CONCAT('CREATE TEMPORARY TABLE mydata AS SELECT ', @mycol, ' FROM foo');
PREPARE stmt FROM @s;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
-- The following select call fails on 2nd and subsequent executions of the SP
SELECT SQL_NO_CACHE * FROM mydata;
SELECT "Please see new temp table mydata" as Result;
END ;;
DELIMITER ;
版本
mysql> SELECT VERSION();
+------------+
| VERSION() |
+------------+
| 5.5.15-log |
+------------+
1 row in set (0.00 sec)
第一次运行按预期工作正常
mysql> CALL mysp(0);
+------+
| col1 |
+------+
| 1 |
| 3 |
| 5 |
+------+
3 rows in set (0.17 sec)
+----------------------------------+
| Result |
+----------------------------------+
| Please see new temp table mydata |
+----------------------------------+
1 row in set (0.17 sec)
Query OK, 0 rows affected (0.17 sec)
现在，如果我尝试使用另一列再次运行它
mysql> CALL mysp(1);
ERROR 1054 (42S22): Unknown column 'qlgqp1.mydata.col1' in 'field list'
mysql> SELECT @mycol;
+--------+
| @mycol |
+--------+
| col2 |
+--------+
1 row in set (0.00 sec)
如果我再次重新创建存储过程它的作品
mysql> CALL mysp(1);
+------+
| col2 |
+------+
| 2 |
| 4 |
| 6 |
+------+
3 rows in set (0.18 sec)
+----------------------------------+
| Result |
+----------------------------------+
| Please see new temp table mydata |
+----------------------------------+
1 row in set (0.18 sec)
Query OK, 0 rows affected (0.18 sec)
但是，如果我尝试切换回第一列 - 即使我尝试先删除临时表 - 它仍然不起作用
mysql> CALL mysp(0);
ERROR 1054 (42S22): Unknown column 'qlgqp1.mydata.col2' in 'field list'
mysql> DROP TABLE mydata;
Query OK, 0 rows affected (0.03 sec)
mysql> CALL mysp(0);
ERROR 1054 (42S22): Unknown column 'qlgqp1.mydata.col2' in 'field list'
mysql>
* Eggyal 要求的其他信息。我也在另一个 mysql 版本上尝试了这个，结果相同。*
mysql> CALL mysp(1);
+------+
| col2 |
+------+
| 2 |
| 4 |
| 6 |
+------+
3 rows in set (0.20 sec)
+----------------------------------+
| Result |
+----------------------------------+
| Please see new temp table mydata |
+----------------------------------+
1 row in set (0.20 sec)
Query OK, 0 rows affected (0.20 sec)
mysql> describe mydata;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| col2 | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.00 sec)
mysql> CALL mysp(0);
ERROR 1054 (42S22): Unknown column 'test.mydata.col2' in 'field list'
mysql> describe mydata;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| col1 | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.00 sec)
有趣的修复开发 - 将最后几行更改为准备好的语句 - 但使用与以前完全相同的查询。
-- The following select call fails on 2nd and subsequent executions of the SP
PREPARE stmt FROM 'SELECT SQL_NO_CACHE * FROM mydata';
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
SELECT "Please see new temp table mydata" as Result;