SQLAlchemy: Ignore SQL's "FOR UPDATE" clause

[surister]

Summary of the changes / Why this is an improvement

Pretty straightforward, now queries like select(table).with_for_update() will not generate a FOR UPDATE statement.

Resolves crate/sqlalchemy-cratedb#95.

Checklist

• Link to issue this PR refers to (if applicable):
• CLA is signed

[amotl]

Thank you very much!

[matriv]

Thx a lot for the PR @surister!
I have the same consideration with #582. SELECT... FOR UPDATE has transactional semantics for traditional RDBMS which CRATEDB doesn't support, shouldn't we somehow make inform the user about an unsupported query (log warning message) or at least add this in docs?

[amotl]

Good point about the user warning, @matriv. I've just added a corresponding improvement to the other patch with 154d77a. If you would be so kind to adjust the patch like that, @surister? 🙏

I think it will be good like this. If you insist on adding it also to the documentation, I can take this, so we do not need to bother @surister about finding a good spot ;].

[matriv]

I think that logging a warning is enough, mainly for those users that quickly try out CrateDB as their backend (switching from some other DB), to be informed.

People working with CrateDB should already know it doesn't support transactions, so adding a docs entry about that to the python client is a bit too much, so I think it's fine to just log a warning.

[amotl]

Thanks. I've amended the patch by adding a similar warning like on the other one.

[amotl]

Dear @surister,

after bringing in #582 and #583, I am going to wrap this up, if you don't have any objections. Users are waiting for another release, and my intention was only to bring in a few small maintenance updates and little improvements like this.

Your contribution was a perfect fit for that, and arrived just in time. Thank you again.

With kind regards,
Andreas.

[matriv]

LGTM. Thank you both @surister and @amotl