sql: cannot perform other schema changes concurrently with alter column type

[Richard Cai]

Currently, ALTER COLUMN TYPE cannot be performed concurrently with other schema changes.

For example you cannot add a column while an alter column type is occuring, you cannot alter primary key while alter column type is occuring.

Jira issue: CRDB-5036

Epic CRDB-25314

[Richard Cai]

#49351 covers this

[Rafi Shamim]

re-opening, since this is referenced here:

cockroach/pkg/sql/alter_column_type.go

Line 220 in 4b8a9c7

 47137, "table %s is currently undergoing a schema change", tableDesc.Name) 

[ajwerner]

I feel like this isn't really about wanting the operations to occur concurrently, it's about wanting them to be ordered.