I am using SQLite3. I load a table with say 30 rows using integer as Primary ID and it auto-increments.
Now I delete all the rows from the table and then, reload some new information onto the table.
Problem is: the row count (my PrimaryID) now starts with 31. Is there any way that I can start loading new rows from the number 1 onwards?
SQLite
Use:
DELETE FROM your_table;
DELETE FROM sqlite_sequence WHERE name = 'your_table';
Documentation
SQLite keeps track of the largest ROWID that a table has ever held using the special SQLITE_SEQUENCE table. The SQLITE_SEQUENCE table is created and initialized automatically whenever a normal table that contains an AUTOINCREMENT column is created. The content of the SQLITE_SEQUENCE table can be modified using ordinary UPDATE, INSERT, and DELETE statements. But making modifications to this table will likely perturb the AUTOINCREMENT key generation algorithm. Make sure you know what you are doing before you undertake such changes.
Found the answer on SO: SQLite Reset Primary Key Field
MySQL
Use:
ALTER TABLE tbl AUTO_INCREMENT = 1;
In either case, the database doesn't care if the id numbers are sequencial - only that the values are unique. If users never see the primary key value (they shouldn't, because the data can change & won't always be at that primary key value), I wouldn't bother with these options.
For MySQL:
Use TRUNCATE TABLE tablename to empty the table (delete all records) and reset auto increment count.
You can also use ALTER TABLE tablename AUTO_INCREMENT = 0; if you just want to reset the count.
For SQLite:
DELETE FROM tablename;
DELETE FROM SQLITE_SEQUENCE WHERE name='tablename';
References
SQLite AutoIncrement
MySQL AutoIncrement
For SQLite use (not need to delete and create the table)
UPDATE SQLITE_SEQUENCE SET SEQ=0 WHERE NAME='table_name';
For MySql use
ALTER TABLE table_name AUTO_INCREMENT = 1;
You should not use AUTOINCREMENT in this case. Simply define your primary key as INTEGER PRIMARY KEY and the count will be reset to 1 after a DELETE FROM query. Without AUTOINCREMENT, the default behaviour will still be an automatic increment of the primary key as long as you don't run out of space in your table (in that case, old - deleted - values will be reused).
More information available in the SQLite Autoincrement document.
ALTER TABLE tbl AUTO_INCREMENT = 0;
Related
I have an old MS Access DB which I'm translating to a MySQL DB. I used bullzip to create the database but due to bad design the old MS Access database didn't have a unique primary key for most of the tables.
So I've created a id field but obviously it's empty for each entry, I wonder if there's a simple statement I can use to fill them up with 1, 2, 3, 4 etc...
EDIT:
I think I haven't gotten my question across properly. I know all about auto increment. Thats not the problem.
I have a table, full of records which I need kept and which came from a Access database that didn't have a unique id defined as a field. In otherwords I have fields for firstname, surname etc etc but no field 'id'. This seems absolutely crazy but apparently this database has been well used and never had any unique ids for any tables bar one. Weird!
Anyway, I've created a field in the table for id (and set it to auto increment of course) but obviously all the existing records don't have an id set currently. So I need to create one for each record.
Is there a way to fill all these records with unique numbers using a mysql statement?
Cheers
If you add an new id column to an existing table and make it AUTO_INCREMENT PRIMARY KEY, it will automatically populate it with incrementing values.
mysql> ALTER TABLE TheTable ADD COLUMN id INT AUTO_INCREMENT PRIMARY KEY;
mysql> SELECT id FROM TheTable;
-- outputs values 1, 2, 3, etc.
If you made an id column but didn't declare it AUTO_INCREMENT PRIMARY KEY, you can populate the column like this:
mysql> SET #id := 0;
mysql> UPDATE TheTable SET id = (#id := #id+1);
Use a predefined AUTO_INCREMENT field, and set the value as NULL when inserting new records, so that it automatically builds up an appropriate incrementer. Aside from that, there is no way (unless using a procedure) to create an incrementing set of values
Use the auto_increment feature of MySQL. MySQL will generate unique numbers for your id column.
For an explanation of the auto_increment feature see http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html
If you just want a unique identifier, you can use the uuid() function. It takes up a bit more space than an integer, but it does what you want.
However, I agree with the other answers that you should add an auto increment column and repopulate the table. That is the simplest way to keep the ids unique over time, even as updates takes place, and using a more reasonable amount of storage.
I am not proficient in MySQL, but I have faced this same problem in other DBMS's and here is how I have addressed it when there was an AutoIncrement type facility, but the DBMS had no way to automatically apply it retroactively:
Rename the table you want to add the ID field to. So rename Table1 to Table1_Old.
Create a new Table1 that is a copy of Table1_Old except that it has no data in it.
Add your ID/AutoIncrement column to Table1
Now copy all of the data from Table1_Old to Table1, either skipping or specifying NULL for the ID column. (This is usually a single INSERT..SELECT.. command)
Drop Table1_Old.
The actual specifics and commands vary from DBMS to DBMS, but I have usually been able to find a way to do these steps.
Use AUTO_INCREMENT
CREATE TABLE insect
(
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
PRIMARY KEY (id),
name VARCHAR(30) NOT NULL,
date DATE NOT NULL,
origin VARCHAR(30) NOT NULL
);
Update
I believe, it seems tough task unless you won't create new table, I will suggest you to use this
SET #rank=0;
SELECT #rank:=#rank+1 AS rank, itemID FROM orders;
It will create a virtual column with the name rank for you, which have unique id value.
I've been using InnoDB for a project, and relying on auto_increment. This is not a problem for most of the tables, but for tables with deletion, this might be an issue:
AUTO_INCREMENT Handling in InnoDB
particularly this part:
AUTO_INCREMENT column named ai_col: After a server startup, for the first insert into a table t, InnoDB executes the equivalent of this statement:
SELECT MAX(ai_col) FROM t FOR UPDATE;
InnoDB increments by one the value retrieved by the statement and assigns it to the column and to the auto-increment counter for the table.
This is a problem because while it ensures that within the table, the key is unique, there are foreign keys to this table where those keys are no longer unique.
The mysql server does/should not restart often, but this is breaking. Are there any easy ways around this?
If you have a foreign key constraint, how can you delete a row from table A when table B references that row? That seems like an error to me.
Regardless, you can avoid the reuse of auto-increment values by resetting the offset when your application starts back up. Query for the maximum in all the tables that reference table A, then alter the table above that maximum, e.g. if the max is 989, use this:
alter table TableA auto_increment=999;
Also beware that different MySQL engines have different auto-increment behavior. This trick works for InnoDB.
So you have two tables:
TableA
A_ID [PK]
and
TableB
B_ID [PK]
A_ID [FK, TableA.A_ID]
And in TableB, the value of A_ID is not unique? Or is there a value in TableB.A_ID that is not in TableA.A_ID?
If you need the value of TableB.A_ID to be unique, then you need to add a UNIQUE constraint to that column.
Or am I still missing something?
Use a foreign key constraint with 'SET NULL' for updates and deletes.
Create another table with a column that remembers the last created Id. This way you don't have to take care of the max values in new tables that have this as foreign key.
I checked.
alter table TableA auto_increment=1;
does NOT work.
And the reason I found in two documents
http://docs.oracle.com/cd/E17952_01/refman-5.1-en/innodb-auto-increment-handling.html
InnoDB uses the following algorithm to initialize the auto-increment counter for a table t that contains an AUTO_INCREMENT column named ai_col: After a server startup, for the first insert into a table t, InnoDB executes the equivalent of this statement:
SELECT MAX(ai_col) FROM t FOR UPDATE;
InnoDB increments the value retrieved by the statement and assigns it to the column and to the auto-increment counter for the table. By default, the value is incremented by one. This default can be overridden by the auto_increment_increment configuration setting.
and
http://docs.oracle.com/cd/E17952_01/refman-5.1-en/alter-table.html
You cannot reset the counter to a value less than or equal to any that have already been used.
This is the reason why alter table will not work. I think that only option is to wipe out data and rewrite it in a new table with new id.
In my case table was logfile , so I just did:
RENAME TABLE SystemEvents To SystemEvents_old;
CREATE TABLE SystemEvents LIKE SystemEvents_old;
I am using an artificial primary key for a table. The table had two columns, one is the primary key and the other one is a Dates (datatype: Date) column. When I tried to load bulk data from a file (which contained values for the second column only), the YYYY part of the dates were added to the primary key column (which was the first column in the table) and the rest of the date was truncated.
So I needed to reset the table. I tried it using the Truncate table statement, but it failed with an error because this table was referenced in the foreign key constraint of another table. So I had to do it using the delete * from table; statement. I did delete all the records, but then when I inserted the records again (using the insert into statement this time), it started incrementing the ID starting from the year after the last year in the year I had previously inserted (i.e. it did not refresh it).
NOTE:- I am using MySQL 5.5 and InnoDB engine.
MY EFFORT SO FAR:-
I tried ALTER TABLE table1 AUTO_INCREMENT=0; (Reference Second Answer) ---> IT DID NOT HELP.
I tried ALTER TABLE table1 DROP column; (Reference- answer 1) ---> Error on rename of table1
Deleted the table again and tried to do:
DBCC CHECKIDENT('table1', RESEED, 0);
(Reference) ---> Syntax error at "DDBC" - Unexpected INDENT_QUOTED
(This statement is right after the delete table statement, if that
matters)
In this article, under the section named "Auto Increment Columns for INNODB Tables" and the heading "Update 17 Feb 2009:", it says that in InnoDB truncate does reset the AUTO_INCREMENT index in versions higher than MySQL 4.1... So I want some way to truncate my table, or do something else to reset the AUTO_INCREMENT index.
QUESTION:-
Is there a way to somehow reset the auto_increment when I delete the data in my table?
I need a way to fix the aforementioned DDBC CHECKINDENT error, or somehow truncate the table which has been referenced in a foreign key constraint of another table.
Follow below steps:
Step1: Truncate table after disabling foreign key constraint and then again enable-
set foreign_key_checks=0;
truncate table mytable;
set foreign_key_checks=1;
Step2: Now at the time of bulk uploading select columns in table only those are in your csv file means un-check rest one (auto id also) and make sure that colums in csv should be in same order as in your table. Also autoid columns should not in your csv file.
You can use below command to upload data.
LOAD DATA LOCAL INFILE '/root/myfile.csv' INTO TABLE mytable fields terminated by ',' enclosed by '"' lines terminated by '\n' (field2,field3,field5);
Note: If you are working in windows environment then change accordinglyl.
You can only reset the auto increment value to 1 (not 0). Therefore, unless I am mistaken you are looking for
alter table a auto_increment = 1;
You can query the next used auto increment value using
select auto_increment from information_schema.tables where
table_name='a' and table_schema=schema();
(Do not forget to replace 'a' with the actual name of your table).
You can play around with a test database (it is likely that your MySQL installation already has a database called test, otherwise create it using create database test;)
use test;
create table a (id int primary key auto_increment, x int); -- auto_increment = 1
insert into a (x) values (1), (42), (43), (12); -- auto_increment = 5
delete from a where id > 1; -- auto_increment = 5
alter table a auto_increment = 2; -- auto_increment = 2
delete from a;
alter table a auto_increment = 1; -- auto_increment = 1
I have a table called Person in MySQL. There is a column id which has UNIQUE and AUTO_INCREMENT property and also a primary key. I want to reset the counter of id so that it restarts from 1. I used the following SQL statement:
ALTER TABLE Person AUTO_INCREMENT=1;
But after I applied this change, the id still starts from my last position (130), not from 1. So why this resetting doesn't work?
Use TRUNCATE TABLE as this will reset the autoincrement
From the documentation...
From MySQL 5.0.13 on, the AUTO_INCREMENT counter is reset to zero by TRUNCATE TABLE, regardless of whether there is a foreign key constraint.)
Right now I have my ID field as the primary key in MySQL and have AUTO_INCREMENT on. What I want to know is how to make the ID represent the number of that row in the table rather than giving it a number when it's inserted, then sticking with that number? Because when I delete something, then that number isn't used. I want them all to be unique based on row count.
Always have a primary key. Either a basic auto increment int or a composite key of multiple fields. It helps your DB do it's job and comes in handy when you want to have relationships. Add a field called RowIndex and renumber it when you delete anything.
When you create a table don't add the AUTO_INCREMENT key word
For existing table, use
ALTER TABLE <Table_Name> MODIFY COLUMN <Column_Name> INTEGER;
to remove the AUTO_INCREMENT and the Primary key will be kept.