Alter table command is not a part of the ANSI standard, but is widely available. Its form is fairly consistent, although its capabilities vary considerably.

It didn't. When created, it was never expected to become a popular and fairly mainstream system. Linux wasn't used commercially until the design had already matured considerably.

Yes; if the "ly" ending didn't give it away, it's used to modify adjectives: considerably larger, considerably cheaper, etc.

Glasses vary very considerably in size.

Glasses vary very considerably in size.

Glasses vary very considerably in size.

Glasses vary very considerably in size.

We are considerably older than our children.