[MDEV-9337] ALTER from DECIMAL and INT to DATETIME returns a wrong result Created: 2015-12-28  Updated: 2016-01-11  Resolved: 2016-01-11

Status: Closed
Project: MariaDB Server
Component/s: Temporal Types
Affects Version/s: 5.5, 10.0, 10.1
Fix Version/s: 10.2.0

Type: Bug Priority: Major
Reporter: Alexander Barkov Assignee: Alexander Barkov
Resolution: Fixed Votes: 0
Labels: None

Issue Links:
Blocks
blocks MDEV-4912 Data type plugin API version 1 Closed

 Description   

These two scripts:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a DATETIME);
 
INSERT INTO t1 VALUES (1000);
 
SELECT * FROM t1;
 

DROP TABLE IF EXISTS t1,t2;
 
CREATE TABLE t1 (a DATETIME);
 
CREATE TABLE t2 (a INT);
 
INSERT INTO t2 VALUES (1000);
 
INSERT INTO t1 SELECT * FROM t2;
 
SELECT * FROM t1;

return

+---------------------+
 
| a                   |
 
+---------------------+
 
| 2000-10-00 00:00:00 |
 
+---------------------+

This script:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a INT);
 
INSERT INTO t1 VALUES (1000);
 
ALTER TABLE t1 MODIFY a DATETIME;
 
SELECT * FROM t1;

returns a different result:

+---------------------+
 
| a                   |
 
+---------------------+
 
| 0000-00-00 00:00:00 |
 
+---------------------+

All three cases are expected to return the same result.

 Comments   
Comment by Alexander Barkov [ 2015-12-28 ]

The same problem is repeatable with the DECIMAL data type:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a DATETIME);
 
INSERT INTO t1 VALUES (1000.0);
 
SELECT * FROM t1;

and

DROP TABLE IF EXISTS t1,t2;
 
CREATE TABLE t1 (a DATETIME);
 
CREATE TABLE t2 (a DECIMAL(4,0));
 
INSERT INTO t2 VALUES (1000);
 
INSERT INTO t1 SELECT * FROM t2;
 
SELECT * FROM t1;

return

+---------------------+
 
| a                   |
 
+---------------------+
 
| 2000-10-00 00:00:00 |
 
+---------------------+

While this script:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a DECIMAL(4,0));
 
INSERT INTO t1 VALUES (1000);
 
ALTER TABLE t1 MODIFY a DATETIME;
 
SELECT * FROM t1;

returns

+---------------------+
 
| a                   |
 
+---------------------+
 
| 0000-00-00 00:00:00 |
 
+---------------------+

Generated at Thu Feb 08 07:33:54 UTC 2024 using Jira 8.20.16#820016-sha1:9d11dbea5f4be3d4cc21f03a88dd11d8c8687422.