primary key and auto_increment 1

[soundmind]

Hi,

When you create a new table and set one field as auto_increment, does this field automatically become the primary key as well?

I tried modifying a table after I created it, with not much success.

1) I tried changing an existing field to auto_increment, didn't work.

2) I tried changing an existing field to primary key, didn't work.

3) I added a new column and set auto_increment, this worked.

4) Setting column #3 as primary key caused an error.

5) I tried adding a new column as primary key, but didn't work either.

I guess I'm confused about what can be done to an existing table/column and what can't.

Help please?

Thanks!

 

[swampBoogie]

primary key and auto_increment are separate issues. auto_increment is a property for a single column. Primary key is a constraint that applies to the table.

create table t(
  c1 int not null auto_increment, 
  constraint t_primary primary key(c1))
)

If the table does not have a primary key constraint it can be added by using an alter table statement.

 

[tshot]

in continuation to swampBoogie, auto_increment have one property of Primary Key that they are unique. was this a source of confusion ?




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