How Can I delete Contents of A table.. If I have 100 rows in a table and i want to delete all of them without droping a table how would I?
Use DELETE without a WHERE clause:
DELETE FROM tablename
This may fail if you have other tables that refer to it via foreign key references.
Both given answers are correct.
The main difference between
TRUNCATE TABLE tablename
and
DELETE FROM tablename
is that TRUNCATE will reset the auto_increment value back to 1. It may make a difference if things have to be unique.
You can also use TRUNCATE
http://dev.mysql.com/doc/refman/5.0/en/truncate-table.html
http://www.postgresql.org/docs/current/static/sql-truncate.html (Thanks for PostgreSQL link to rfusca)
TRUNCATE TABLE tablename
You can use Truncate also,it's faster than DELETE but TRUNCATE will not work under a table lock or transaction.
have a look at
http://dev.mysql.com/doc/refman/5.0/en/truncate-table.html
http://dev.mysql.com/doc/refman/5.0/en/delete.html
Related
DELETE FROM Orders WHERE OrderID BETWEEN 1 AND 1000;
but if the table record is unknown to me than how can i delete all record from the table without deleting table.
TRUNCATE Orders;
This is all what you need to delete all the content of your selected table
Use "TRUNCATE" syntax.
It will empties a table completely.
Check this document:
http://dev.mysql.com/doc/refman/5.7/en/truncate-table.html
DELETE
When we have to use DELETE Command then the data deleted can be retrieved when you ROLLBACK.
DELETE * FROM Orders;
TRUNCATE
It drops the table and re-create it. It is much faster than deleting
rows one by one. Once you use TRUNCATE command then you cannot retrieve
the data again from the table.
TRUNCATE Orders;
If you want to delete all the records, you can do this with:
TRUNCATE TABLE Orders
The table still exists but will be empty.
But if you want to delete a range of records you could probably do:
DELETE FROM Orders WHERE OrderID BETWEEN 1 AND (SELECT max(OrderID) FROM table)
In the last case all OrderID's must be unique.
Which one will delete all data from the table, and which one will remove the table from the database?
What is the right thing to do if I don't want this table in my database any more?
Should I drop or delete?
DROP command deleting the table and its structure from the data base.
DROP TABLE tbl_user;
DELETE command used for deleting the records from the table,and it removing the table space which is allocated by the data base, and returns number of rows deleted.
DELETE FROM tbl_user WHERE id = 1;
TRUNCATE command is also delete the records but it doesn't delete the table space which is created by the data base, and does not return number of deleted rows.
TRUNCATE TABLE tbl_user;
DROP is used to remove tables (and databases).
DELETE is used to delete rows from tables.
Maybe are you talking about TRUNCATE and DELETE ?
TRUNCATE TABLE users;
is equivalent (logically) to
DELETE FROM users;
This will erase all data in table users. If you want to delete the whole table structure you should write:
DROP TABLE users;
But, DELETE is DML command while TRUNCATE and DROP are DDL commands. There is also some other differences in different RDBMS. More info - here
And another useful link: Difference between TRUNCATE, DELETE and DROP commands
drop removes the contents and the table (but not user permissions on the table). This is what you want if you want to completely remove the table from your schema.
delete selectively (or not) removes rows from a table. It does not alter the table structure.
There's no such thing as DELETE TABLE. You should use DROP TABLE to delete your table.
The DROP TABLE statement is used to delete a table.
DROP TABLE table_name
The DELETE statement is used to delete data(records) in a table.
DELETE FROM table_name WHERE some_column=some_value;
So, as you want to delete table from database then you will go for DROP Command
DELETE is used to delete one or several rows from the table. DROP TABLE would remove the entire table from the database, so if you want to remove the table, you should use DROP TABLE.
DROP TABLE reference
Delete will update the log, while drop does not.
Delete is used to remove the rows, while drop is used to remove the tables and DB.
delete
- removes the rows from the table - where clause can be used to delete specific rows.
- If where is not specified, then all the rows in the table will be removed
- rollback can be done.
without using where condition
DELETE * FROM empl;
using where condition
DELETE FROM empl WHERE job = 'Manager';
truncate
- removes all the rows from the table.
- rollback cannot be done.
SQL> TRUNCATE TABLE empl;
drop
- removes a table from the database.
- rows, indexes and privileges will also be removed.
- rollback cannot be done.
SQL> DROP TABLE empl;
Delete remove all data from a specific table and drop remove whole database and also remove specific table from database.
If you don't want the table in database any more then you should drop the table.
Is it possible to use the LIKE statement on ALTER TABLE similar to CREATE TABLE in MySQL?
Eg. 'CREATE TABLE db.tbl1 LIKE db.tbl2'
This clones a database table's structure. I want to alter an existing table with the same columns but to pick up the primary keys of another table.
I was thinking of something like 'ALTER TABLE db.tbl1 LIKE db.tbl2' but this throws back an error.
Any ideas?
Thanks
I required a similar thing and settled to use the following procedure:
ALTER TABLE tbl1 RENAME tbl1_old;
CREATE TABLE tbl1 LIKE tbl2;
INSERT INTO tbl1 SELECT * FROM tbl1_old;
DROP TABLE tbl1_old;
Altough this is not a single statement it should do the job. Only problem could be different index settings (UNIQUE, etc.) which cause errors when doing the "INSERT INTO" of the original table contents.
Everything ALTER TABLE can do is explained here.
As you can see importing indexes from another table is not mentioned. You could probably do that with some clever information_schema querying, but I don't think it would be worth the cost.
It seems you can't.
I am attempting to clean out a table but not get rid of the actual structure of the table. I have an id column that is auto-incrementing; I don't need to keep the ID number, but I do need it to keep its auto-incrementing characteristic. I've found delete and truncate but I'm worried one of these will completely drop the entire table rendering future insert commands useless.
How do I remove all of the records from the table so that I can insert new data?
drop table will remove the entire table with data
delete * from table will remove the data, leaving the autoincrement values alone. it also takes a while if there's a lot of data in the table.
truncate table will remove the data, reset the autoincrement values (but leave them as autoincrement columns, so it'll just start at 1 and go up from there again), and is very quick.
TRUNCATE will reset your auto-increment seed (on InnoDB tables, at least), although you could note its value before truncating and re-set accordingly afterwards using alter table:
ALTER TABLE t2 AUTO_INCREMENT = value
Drop will do just that....drop the table in question, unless the table is a parent to another table.
Delete will remove all the data that meets the condition; if no condition is specified, it'll remove all the data in the table.
Truncate is similar to delete; however, it resets the auto_increment counter back to 1 (or the initial starting value). However, it's better to use truncate over delete because delete removes the data by each row, thus having a performance hit than truncate. However, truncate will not work on InnoDB tables where referential integrity is enforced unless it is turned off before the truncate command is issued.
So, relax; unless you issue a drop command on the table, it won't be dropped.
Truncate table is what you are looking for
http://www.1keydata.com/sql/sqltruncate.html
Another possibility involves creating an empty copy of the table, setting the AUTO_INCREMENT (with some eventual leeway for insertions during the non-atomic operation) and then rotating both :
CREATE TABLE t2_new LIKE t2;
SELECT #newautoinc:=auto_increment /*+[leeway]*/
FROM information_schema.tables
WHERE table_name='t2';
SET #query = CONCAT("ALTER TABLE t2_new AUTO_INCREMENT = ", #newautoinc);
PREPARE stmt FROM #query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
RENAME TABLE t2 TO t2_old, t2_new TO t2;
And then, you have the extra advantage of being still able to change your mind before removing the old table.
If you reconsider your decision, you can still bring back old records from the table before the operation:
INSERT /*IGNORE*/ INTO t2 SELECT * FROM t2_old /*WHERE [condition]*/;
When you're good you can drop the old table:
DROP TABLE t2_old;
I've just come across a situation where DELETE is drastically affecting SELECT performance compared to TRUNCATE on a full-text InnoDB query.
If I DELETE all rows and then repopulate the table (1million rows), a typical query takes 1s to come back.
If instead I TRUNCATE the table, and repopulate it in exactly the same way, a typical query takes 0.05s to come back.
YMMV, but for whatever reason for me on MariaDB 10.3.15-MariaDB-log DELETE seems to be ruining my index.
I have an enormous MySQL (InnoDB) database with millions of rows in the sessions table that were created by an unrelated, malfunctioning crawler running on the same server as ours. Unfortunately, I have to fix the mess now.
If I try to truncate table sessions; it seems to take an inordinately long time (upwards of 30 minutes). I don't care about the data; I just want to have the table wiped out as quickly as possible. Is there a quicker way, or will I have to just stick it out overnight?
(As this turned up high in Google's results, I thought a little more instruction might be handy.)
MySQL has a convenient way to create empty tables like existing tables, and an atomic table rename command. Together, this is a fast way to clear out data:
CREATE TABLE new_foo LIKE foo;
RENAME TABLE foo TO old_foo, new_foo TO foo;
DROP TABLE old_foo;
Done
The quickest way is to use DROP TABLE to drop the table completely and recreate it using the same definition. If you have no foreign key constraints on the table then you should do that.
If you're using MySQL version greater than 5.0.3, this will happen automatically with a TRUNCATE. You might get some useful information out of the manual as well, it describes how a TRUNCATE works with FK constraints. http://dev.mysql.com/doc/refman/5.0/en/truncate-table.html
EDIT: TRUNCATE is not the same as a drop or a DELETE FROM. For those that are confused about the differences, please check the manual link above. TRUNCATE will act the same as a drop if it can (if there are no FK's), otherwise it acts like a DELETE FROM with no where clause.
EDIT: If you have a large table, your MariaDB/MySQL is running with a binlog_format as ROW and you execute a DELETE without a predicate/WHERE clause, you are going to have issues to keep up the replication or even, to keep your Galera nodes running without hitting a flow control state. Also, binary logs can get your disk full. Be careful.
The best way I have found of doing this with MySQL is:
DELETE from table_name LIMIT 1000;
Or 10,000 (depending on how fast it happens).
Put that in a loop until all the rows are deleted.
Please do try this as it will actually work. It will take some time, but it will work.
Couldn't you grab the schema drop the table and recreate it?
drop table should be the fastest way to get rid of it.
Have you tried to use "drop"? I've used it on tables over 20GB and it always completes in seconds.
If you just want to get rid of the table altogether, why not simply drop it?
Truncate is fast, usually on the order of seconds or less. If it took 30 minutes, you probably had a case of some foreign keys referencing the table you were truncating. There may also be locking issues involved.
Truncate is effectively as efficient as one can empty a table, but you may have to remove the foreign key references unless you want those tables scrubbed as well.
We had these issues. We no longer use the database as a session store with Rails 2.x and the cookie store. However, dropping the table is a decent solution. You may want to consider stopping the mysql service, temporarily disable logging, start things up in safe mode and then do your drop/create. When done, turn on your logging again.
I'm not sure why it's taking so long. But perhaps try a rename, and recreate a blank table. Then you can drop the "extra" table without worrying how long it takes.
searlea's answer is nice, but as stated in the comments, you lose the foreign keys during the fight.
this solution is similar: the truncate is executed within a second, but you keep the foreign keys.
The trick is that we disable/enable the FK checks.
SET FOREIGN_KEY_CHECKS=0;
CREATE TABLE NewFoo LIKE Foo;
insert into NewFoo SELECT * from Foo where What_You_Want_To_Keep
truncate table Foo;
insert into Foo SELECT * from NewFoo;
SET FOREIGN_KEY_CHECKS=1;
Extended answer - Delete all but some rows
My problem was: Because of a crazy script, my table was for with 7.000.000 junk rows. I needed to delete 99% of data in this table, this is why i needed to copy What I Want To Keep in a tmp table before deleteting.
These Foo Rows i needed to keep were depending on other tables, that have foreign keys, and indexes.
something like that:
insert into NewFoo SELECT * from Foo where ID in (
SELECT distinct FooID from TableA
union SELECT distinct FooID from TableB
union SELECT distinct FooID from TableC
)
but this query was always timing out after 1 hour.
So i had to do it like this:
CREATE TEMPORARY TABLE tmpFooIDS ENGINE=MEMORY AS (SELECT distinct FooID from TableA);
insert into tmpFooIDS SELECT distinct FooID from TableB
insert into tmpFooIDS SELECT distinct FooID from TableC
insert into NewFoo SELECT * from Foo where ID in (select ID from tmpFooIDS);
I theory, because indexes are setup correctly, i think both ways of populating NewFoo should have been the same, but practicaly it didn't.
This is why in some cases, you could do like this:
SET FOREIGN_KEY_CHECKS=0;
CREATE TABLE NewFoo LIKE Foo;
-- Alternative way of keeping some data.
CREATE TEMPORARY TABLE tmpFooIDS ENGINE=MEMORY AS (SELECT * from Foo where What_You_Want_To_Keep);
insert into tmpFooIDS SELECT ID from Foo left join Bar where OtherStuff_You_Want_To_Keep_Using_Bar
insert into NewFoo SELECT * from Foo where ID in (select ID from tmpFooIDS);
truncate table Foo;
insert into Foo SELECT * from NewFoo;
SET FOREIGN_KEY_CHECKS=1;