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Bug#19025 4.1 mysqldump doesn't correctly dump "auto_increment = [int]"

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mysqldump / SHOW CREATE TABLE will show the NEXT available value for
the PK, rather than the *first* one that was available (that named in
the original CREATE TABLE ... AUTO_INCREMENT = ... statement).

This should produce correct and robust behaviour for the obvious use
cases -- when no data were inserted, then we'll produce a statement
featuring the same value the original CREATE TABLE had; if we dump
with values, INSERTing the values on the target machine should set the
correct next_ID anyway (and if not, we'll still have our AUTO_INCREMENT =
... to do that). Lastly, just the CREATE statement (with no data) for
a table that saw inserts would still result in a table that new values
could safely be inserted to).

There seems to be no robust way however to see whether the next_ID
field is > 1 because it was set to something else with CREATE TABLE
... AUTO_INCREMENT = ..., or because there is an AUTO_INCREMENT column
in  the table (but no initial value was set with AUTO_INCREMENT = ...)
and then one or more rows were INSERTed, counting up next_ID. This
means that in both cases, we'll generate an AUTO_INCREMENT =
... clause in SHOW CREATE TABLE / mysqldump.  As we also show info on,
say, charsets even if the user did not explicitly give that info in
their own CREATE TABLE, this shouldn't be an issue.

As per above, the next_ID will be affected by any INSERTs that have
taken place, though.  This /should/ result in correct and robust
behaviour, but it may look non-intuitive to some users if they CREATE
TABLE ... AUTO_INCREMENT = 1000 and later (after some INSERTs) have
SHOW CREATE TABLE give them a different value (say, CREATE TABLE
... AUTO_INCREMENT = 1006), so the docs should possibly feature a
caveat to that effect.

It's not very intuitive the way it works now (with the fix), but it's
*correct*.  We're not storing the original value anyway, if we wanted
that, we'd have to change on-disk representation?

If we do dump/load cycles with empty DBs, nothing will change.  This
changeset includes an additional test case that proves that tables
with rows will create the same next_ID for AUTO_INCREMENT = ... across
dump/restore cycles.

Confirmed by support as likely solution for client's problem.
This commit is contained in:
tnurnberg@mysql.com
2006-05-04 03:12:51 +02:00
parent b695bb4624
commit 5becb110e0
7 changed files with 134 additions and 5 deletions
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24
mysql-test/r/auto_increment.result
View File

@@ -355,3 +355,27 @@ CHECK TABLE t1;
Table Op Msg_type Msg_text
test.t1 check status OK
DROP TABLE IF EXISTS t1;
CREATE TABLE `t1` (
t1_name VARCHAR(255) DEFAULT NULL,
t1_id INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
KEY (t1_name),
PRIMARY KEY (t1_id)
) AUTO_INCREMENT = 1000;
INSERT INTO t1 (t1_name) VALUES('MySQL');
INSERT INTO t1 (t1_name) VALUES('MySQL');
INSERT INTO t1 (t1_name) VALUES('MySQL');
SELECT * from t1;
t1_name t1_id
MySQL 1000
MySQL 1001
MySQL 1002
SHOW CREATE TABLE `t1`;
Table Create Table
t1 CREATE TABLE `t1` (
`t1_name` varchar(255) default NULL,
`t1_id` int(10) unsigned NOT NULL auto_increment,
PRIMARY KEY (`t1_id`),
KEY `t1_name` (`t1_name`)
) ENGINE=MyISAM AUTO_INCREMENT=1003 DEFAULT CHARSET=latin1
DROP TABLE `t1`;
End of 4.1 tests