How to modify a column to insert consequtive numbers? - mysql

Question

So I have a table where a column that was given an auto_increment value accidentally got started form 300 instead of 1,2,3,4......i'm a beginner and i do not know how to change it back to 1,2,3,4......screenshot of table
how to change the 307, 308 to 1,2,3,4...?
I tried to update the table but that did not work.

Answer 1

Step-1) First take backup of your table data.
Step-2) Truncate the table by using the below SQL query.
TRUNCATE TABLE [Your_Table_Name];
Step-3) then again insert the into your table using backup data.

Answer 2

Alter table to drop the auto_increment, update, alter table to add the auto_increment
drop table if exists t;
create table t
( id int auto_increment primary key, val int);
insert into t values
(307,1),(308,1),(309,1),(310,1),(311,1);
alter table t
modify column id int;
#drop primary key;
show create table t;
update t
set id = id - 306;
alter table t
modify column id int auto_increment;
show create table t;
https://dbfiddle.uk/eBQh6cj8

Answer 3

With MySQL 8.0 you can use a window function to calculate the row numbers and then update the table:
mysql> select * from t;
+-----+------+
| id | val |
+-----+------+
| 307 | 1 |
| 308 | 1 |
| 309 | 1 |
| 310 | 1 |
| 311 | 1 |
+-----+------+
mysql> with cte as ( select id, row_number() over () as rownum from t )
-> update t join cte using (id) set id = rownum;
Query OK, 5 rows affected (0.00 sec)
Rows matched: 5 Changed: 5 Warnings: 0
mysql> select * from t;
+----+------+
| id | val |
+----+------+
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 1 |
+----+------+
Then make sure the next id won't be a high value:
mysql> alter table t auto_increment=1;
You can try to set the auto_increment to 1, MySQL will automatically advances that to the highest id value in the table, plus 1.
Be aware that this doesn't guarantee subsequent rows will use consecutive values. You can get non-consecutive values if:
You insert greater values explicitly, overriding the auto-increment.
You roll back transactions. Id values generated by auto-increment are not recycled if you roll back.
You delete rows.
Occasionally InnoDB will skip a number anyway. It does not guarantee consecutive values — it only guarantees unique values. You should not rely on the auto-increment to be the same as a row number.

Answer 4

Here is a one approach to your problem.
Please take note of the following points before proceeding:
Take backup of your table in-case things do not go as expected.
Below test case has been performed on MySQL 5.7 and MyISAM Engine.
Step1: Generating dummy test table as per your test case.
mysql> CREATE TABLE t (
-> `Id` int(11) NOT NULL AUTO_INCREMENT,
-> `product_id` int(11) DEFAULT 0,
-> PRIMARY KEY (`Id`)
-> ) ENGINE=MyISAM;
Query OK, 0 rows affected (0.03 sec)
-- Inserting dummy data
mysql> INSERT INTO t VALUES (300,1);
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO t VALUES (302,1);
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO t VALUES (305,1);
Query OK, 1 row affected (0.00 sec)
-- Checking auto_increment value
mysql> show create table t;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t | CREATE TABLE `t` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`product_id` int(11) DEFAULT '0',
PRIMARY KEY (`Id`)
) ENGINE=MyISAM AUTO_INCREMENT=306 DEFAULT CHARSET=latin1 |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> INSERT INTO t (product_id) VALUES (2);
Query OK, 1 row affected (0.01 sec)
-- Below is the resultant table for which we need Id starting from 1,2,3 and so on...
mysql> SELECT * FROM t;
+-----+------------+
| Id | product_id |
+-----+------------+
| 300 | 1 |
| 302 | 1 |
| 305 | 1 |
| 306 | 2 |
+-----+------------+
4 rows in set (0.00 sec)
Step2: Remove AUTO_INCREMENT for the column and set the Ids manually.
-- Remove AUTO_INCREMENT
mysql> ALTER TABLE t MODIFY COLUMN Id int(11) NOT NULL;
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
-- Set the Id manually starting from 1
mysql> SET #i = 0;UPDATE t SET id = #i :=#i +1;
Query OK, 0 rows affected (0.00 sec)
Query OK, 5 rows affected (0.00 sec)
Rows matched: 5 Changed: 5 Warnings: 0
-- Below is the updated table with Id starting from 1,2,3 and so on...
mysql> SELECT * FROM t;
+----+------------+
| Id | product_id |
+----+------------+
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 2 |
+----+------------+
5 rows in set (0.00 sec)
Step3: Enable AUTO_INCREMENT again for future record insertions.
-- Enable AUTO_INCREMENT again for future record insertions.
mysql> ALTER TABLE t MODIFY COLUMN Id int(11) NOT NULL AUTO_INCREMENT;
Query OK, 5 rows affected (0.01 sec)
Records: 5 Duplicates: 0 Warnings: 0
-- Set the AUTO_INCREMENT value to continue from highest value of id in the table.
mysql> SELECT MAX(id+1) FROM t;
+-----------+
| MAX(id+1) |
+-----------+
| 6 |
+-----------+
1 row in set (0.00 sec)
mysql> ALTER TABLE t AUTO_INCREMENT=6;
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
-- Table is successfully modified and will have future records inserted with no gaps in Id's
mysql> INSERT INTO t (product_id) VALUES (5);
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM t;
+----+------------+
| Id | product_id |
+----+------------+
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 2 |
| 6 | 5 |
+----+------------+
6 rows in set (0.00 sec)

Answer 5

The DBCC CHECKIDENT management command is used to reset identity counter
DBCC CHECKIDENT (table_name [, { NORESEED | { RESEED [, new_reseed_value]}}])
[ WITH NO_INFOMSGS ]
EXample:
DBCC CHECKIDENT ('TestTable', RESEED, 0)
GO
many times we need to just reseed to next Id available
declare #max int
select #max=max([Id]) from [TestTable]
if #max IS NULL --check when max is returned as null
SET #max = 0
DBCC CHECKIDENT ('[TestTable]', RESEED, #max)
This will check the table and reset to the next ID.
You can get help from the link below:
Reset identity seed after deleting records in SQL Server
My mother says: the mountain that can be seen is not far away, don't stop trying