Drop Column from Large Table

Question

I have this largish table with three columns as such:

+-----+-----+----------+
| id1 | id2 | associd  |
+-----+-----+----------+
|   1 |  38 | 73157604 |
|           


        

Answer 1

Anything that you do is going to require reading and writing 38m rows, so nothing is going to be real fast. Probably the fastest method is probably to put the data into a new table:

create table newTable as
    select id1, id2
    from oldTable;

Or, if you want to be sure that you preserve types and indexes:

create table newTable like oldTable;

alter table newTable drop column assocId;

insert into newTable(id1, id2)
    select id1, id2
    from oldTable;

However, it is usually faster to drop all index on a table before loading a bunch of data and then recreate the indexes afterwards.