If the auto_increment column is part of multiple indexes, mysql generates sequence values using the index that begins with the auto_increment column, if there is one. for example, if the animals table contained indexes primary key (grp, id) and index (id) , mysql would ignore the primary key for generating sequence values.. Yes, you can use the alter table t auto_increment = 42 statement. however, you need to be aware that this will cause the rebuilding of your entire table, at least with innodb and certain mysql versions.. Similar to mysql, postgresql, oracle, and many other relational databases, sql server is best utilized when assigning unique primary keys to most database tables..
To add a new auto_increment integer column named c: alter table t2 add c int unsigned not null auto_increment, add primary key (c); we indexed c (as a primary key) because auto_increment columns must be indexed, and we declare c as not null because primary key columns cannot be null.. If the auto_increment column is part of multiple indexes, mysql generates sequence values using the index that begins with the auto_increment column, if there is one. for example, if the animals table contained indexes primary key (grp, id) and index (id) , mysql would ignore the primary key for generating sequence values.. Mysql: create table persons ( id int not null, lastname varchar(255) not null, to create a primary key constraint on the "id" column when the table is already created, use the following sql: if you use the alter table statement to add a primary key, the primary key column(s).
