Refactor statement matching

[sunng87]

Currently we are using string matching to shortcut those set, show statements. However, this approach somehow fragile. Since we are already using sqlparser for rewrite rules, we can get Statement for both simple and extended query. It would be better to rewrite those shortcut code by check the structured Statement.

[sunng87]

@iPeluwa , do you want to work on this refactoring?

[iPeluwa]

@sunng87 Yes please, I would take a dig at it.

[sunng87]

@iPeluwa Let me know if you have any questions. We can start from the statement at https://github.com/datafusion-contrib/datafusion-postgres/blob/master/datafusion-postgres/src/handlers.rs#L463

[iPeluwa]

#164, I would create a follow-up PR that would completely remove the deprecated methods and update all remaining test references. But the core goal is achieved - robust, type-safe statement handling 🎉

[iPeluwa]

@sunng87 I'm back now and can attend to this, I was away due to a little health issue.

[sunng87]

Thank you @iPeluwa . Hope everything is well now. Just take your time.

[sunng87]

@mjgarton already made refactoring in #211 and #213.

Next we will move transaction statements to QueryHook and replace string with statement matching.

[iPeluwa]

Okay great, I can take on that and have it merged by morrow @sunng87

[sunng87]

Sure, thank you @iPeluwa