mysql - Add auto_increment unique id to my sql? -

i have created table in mysql , want add column i.e, 'myid' table i.e, 'mytable'.

there primary key defined.

i use follwing query add auto increment:

alter table mytable add myid int unsigned not null auto_increment unique; 

but want auto increment should start 30 rather 1.

what modification query required? other way add this?

secondly if use following procedure,

first run query: alter table mytable auto_increment = 30;

then run alter table mytable add myid int unsigned not null auto_increment unique;

will okay? yes or no?

if table empty or small first add auto_increment column , set it's start value this:

make myid auto_increment column:

alter table `mytable` add `myid` int unsigned not null auto_increment unique; 

set start value 30 alter table mytable auto_increment = 30;

caveat

if have lots of records in mytable , use

alter table mytable auto_increment = 30; 

mysql server create new table, copy data old table new, delete old , rename new 1 though there no structural change table. server response show rows have been affected this:

mysql> alter table mytable auto_increment = 30; query ok, 609481 rows affected (1 min 4.55 sec) records: 609481 duplicates: 0 warnings: 0

there potential issues may arise table copy e.g. insufficient amount of free disk space second copy of data.

trick can use insert dummy row , explicitly set auto_increment column 29, delete dummy row. next row inserted start @ 30 , values go upwards there.