Hi I have Amazon rds which i can connect to using the mysql prompt
I want to empty a table using the prompt command line
What's the best way to do the above? Thanks!
You can use the standard truncate command to empty the required tables. If you want to truncate multiple tables follow this question.
Try
DELETE FROM `table_name`;
Notice the missing where clause, this will delete all rows.
Data can't be deleted that's connected by a constraint.
What you need is code that first removes constraints, then deletes the
data, and finally restores the constraints:
See more at: http://www.devx.com/dbzone/Article/40967#sthash.NUmxsFr3.dpuf
Moreover, use DELETE command as you can ROLLBCK the operation. While using truncate, operation cannot be rolled back and no triggers will be fired
Related
I have a mysql table y in database xxx which I attempted to change compression type before using
alter table y row_format=compressed key_block_size=8
the process stopped half way. I removed temp file '#sql-ib265.frm and #sql-ib265' in mysql lib directory and restarted the server. However
Now when I attempt the alter table y (with the same command above) again I get error.
ERROR 1050 (42S01) at line 1: Table 'xxx/#sql-ib265' already exists
I can't drop table 'xxx/#sql-ib265' because it can't be found.
what should I do?
Edit
Solution:
I ended up dropping the old database and recreate the database.
Try to restart mysql client with the --skip-auto-rehash option and try DROP TABLE again.
If above does not work, try this from MySQL Manual:
You have a corrupt innodb data dictionary..
https://dev.mysql.com/doc/refman/5.0/en/innodb-troubleshooting-datadict.html
Problem with Temporary Table
If MySQL crashes in the middle of an ALTER TABLE operation, you may end up with an orphaned temporary table inside the InnoDB tablespace. Using the Table Monitor, you can see listed a table with a name that begins with #sql-. You can perform SQL statements on tables whose name contains the character “#” if you enclose the name within backticks. Thus, you can drop such an orphaned table like any other orphaned table using the method described earlier. To copy or rename a file in the Unix shell, you need to put the file name in double quotation marks if the file name contains “#”.
There are two ways to fix this problem.
As other answer suggests, official MySQL documentation suggests to drop a specially crafted table. But please note in versions >= 5.1 you need to prefix table name with #mysql50#.
Move (use RENAME TO) all good tables to a temporary database, drop&recreate the original one and then move the tables back. See a blog post for details.
in additional I'm loging in with root to do the recover job but failed. then i chown the .frm file to meet the owner of mysql service and succeed.
For anyone still facing this problem, I have just followed the following steps to solve it, which (to me at least) seem far less daunting than other solutions:
Use mysqldump to back up the database with all its data.
Drop and recreate the database.
Reload the database and all its schema from the file generated in (1).
Because the orphaned tables are hidden anyway, they don't get backed up, so you end up with a database without them. I had all my procedures/functions scripted out anyway, so was able to restore them easily - if you don't, make sure you use the --routines parameter to dump those too.
My dump file was around 1.5GB for the database in question (so it's not small), and the whole thing was completed in a few minutes.
I had the same error. I fixed it by switching the order in which I dropped the tables at the beginning of the file:
DROP TABLE IF EXISTS table_name;
This line is repeated for each table. Tables with foreign keys need to be deleted before the tables with the primary keys to which they point.
I'm doing an update to MySQL Database which includes MySQL scripts that make ALTER TABLE sentences, as well as DIU sentences (delete, insert, update).
The idea is to make a transactional update, so if a sentence fails, a rollback is made, but if I put ALTER TABLE sentences or others specified in http://dev.mysql.com/doc/refman/5.0/en/implicit-commit.html an implicit commit is made, so I can't make a complete rollback, because the indicated operations remains commited.
I tried to use mysqldump to make a backup which is used in case of error (mysql returns distinct to zero), but it is too slow and can fail too.
What can I do? I need this to ensure that future updates are safe and not too slow, because databases contains between 30-100 GB of data.
dump and reload might be your best options instead of alter table.
From mysql prompt or from the database script:
select * from mydb.myt INTO OUTFILE '/var/lib/mysql/mydb.myt.out';
drop table mydb.myt;
create tablemyt(your table ddl here)
load data infile '/var/lib/mysql/mydb.myt.out' INTO TABLE mydb.myt;
Check this out:
http://everythingmysql.ning.com/profiles/blogs/whats-faster-than-alter
I think it offers good guidance on "alternatives to alter".
Look at pt-online-schema change.
You can configure it to leave the 'old' table around after the online ALTER is completed. The old table will have an underscore prefix. If bad things happen, drop the tables you altered and renamed the OLD tables to the original tables. If everything is OK, then just drop the OLD tables.
http://www.percona.com/doc/percona-toolkit/2.1/pt-online-schema-change.html
Once a record is entered in a particular table, I think I don't ever want it to be deleted. The records are there to keep track of things for historical purposes. I'm using MySQL, InnoDB. Is there any way I can protect that table from accidental deletes by the application layer? If so, is this a good approach?
If you can set the permission for your user(s), don't give the delete permission. There're situations where this practice is a "must be" like the tables for statistics purpose. Thus, if your table is used to achieve one of this goal, it's a good approach.
I use a trigger that detects the deletion and does some illegal stuff so the whole operation fails. For example like this:
CREATE TRIGGER protect_delete before delete ON protected_table
FOR EACH ROW UPDATE non_existing_table SET non_existing_column=1;
So when someone will attempt a delete operation - the whole statement will fail. You also might use better names for non_existing_column and non_existing_table.
E.g it is possible to obtain an error message like this:
ERROR 1146 (42S02): Table 'database.delete_restricted_on_tableX'
doesn't exist
EDIT: also it is possible to create even better fail messages, please check here http://www.brokenbuild.com/blog/2006/08/15/mysql-triggers-how-do-you-abort-an-insert-update-or-delete-with-a-trigger/
One other option is switch to the ARCHIVE engine for historical tables.
This will prevent any DELETE or UPDATE actions on the table, and compress the data. One (major) downside to this approach is that you cannot index the columns on the table.
I think you should implement this logic in your application layer and insert a column where you put a no-delete flag.
Another idea would be to exclude the delete access for the db user
You may want to write a trigger that detects the deletion, then reinserts the record, but there may be some issues with that, so you can also just add a foreign key constraint that will prevent the deletion.
For some discussions on this you can look at: http://rpbouman.blogspot.com/2011/10/mysql-hacks-preventing-deletion-of.html.
I am fairly new to using mysql. I have an application that performs some basic querying. I am also trying to run a simple delete statement -
delete from mydb.mytable
This table is a simple 2 column table with not keys or triggers or anything defined. For some reason, the delete is not being performed. If I run the statement from MySql Workbench in the query window, it works fine. From the code, it does nothing. I am not seeing any error messages. I created a user with select, insert, update and delete rights to the schema. I am able to do the insert fine, but the delete does not seem to be working.
Is there a setting for mysql that I am missing that will not allow me to perform the delete?
Thanks for any thoughts.
Fist of all, check if
you are connected to the right database ;
you are using transaction and forgetting 'commit' ;
the user you use have enough permissions to delete from the table .
As a side notice, if you want to delete all records, you should use truncate instead of delete
Are you using transactions? My first guess is that your code might be issuing a BEGIN TRANSACTION without a COMMIT.
We would have to see some of your code to answer the question.
My guess is that you are not calling commit from your code. You can configure MySQL to auto-commit your queries, but this is usually not what you want.
I have a MySQL script which is executed automatically under certain conditions. That script executes an ALTER TABLE command, because that column is needed in the database, but it may or may not have it...
Is it possible to make MySQL 4 execute the ALTER TABLE statement if the column doesn't exist or ignore the duplicate column error for this single command and allow the script execution to continue?
ALTER [IGNORE] TABLE will only ignore certain errors, like duplicate key errors when adding a new UNIQUE index, or SQL mode errors.
http://dev.mysql.com/doc/refman/4.1/en/alter-table.html
More details about the "script" you are using would help to answer the question. In python for example, the error would raise an exception which could then be caught and dealt with or ignored.
[EDIT] From the comment below, seems like you're looking for the mysql -f command line option.
You can first check the table schema before you attempt an addition of the column? However , I strongly suspect the design where you need to add columns on the fly. Something is not quite right. Can you explain the requirement in a little detail. I'm sure there are other cleaner way around this.