fix: isWriteType() to recognize CTE; always excluding RETURNING

[markconnellypro]

Description

This pull request attempts to fix some issues I ran into with queries being miscategorized as isWriteType or not, particularly with PostgreSQL:

• Operations with CTE (flagged by WITH) were not being counted as isWriteType, even if followed by an appropriate operator like INSERT/UPDATE.
• In Postgre, INSERT/UPDATE operations with RETURNING were being counted as isWriteType if there was whitespace before INSERT/UPDATE.
• In Postgre, DELETE operations with RETURNING were always being counted as isWriteType.

Edit: this pull request has been modified to remove the Postgre override of isWriteType, and to incorporate RETURNING handling in isWriteType on a uniform basis for all database types.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

Thank you!
Please fix coding style. Run composer cs-fix.

[kenjis]

WriteTypeQueryTest is not a good test code to begin with. Do not use it as a reference.
One test method should not contain multiple assertions.
It becomes difficult to understand what you want to test.

[kenjis]

@markconnellypro Can you add new test methods to test WITH clause on Postgre, instead of adding tests to the existing methods?

[markconnellypro]

Each test is now in its own function. The code for determining whether CodeIgniter supports RETURNING is now centralized in one function, so that any future expansions of functionality only need to be fixed in one location, instead of in 15. (To separate out Postgre, I would have had to add an additional 15 tests.)

[kenjis]

Do you know why "? is needed?

[markconnellypro]

I don't, but since it was already there, I left it.

[kenjis]

Yes, it came from CI3.
https://github.com/bcit-ci/CodeIgniter/blob/70d0a0edbee5e5814aefddb77f67628e68de080f/system/database/DB_driver.php#L999
So it is not easy to remove it.

But I don't imagine a use case. And it seems there is no test case for it.

[kenjis]

Thank you! The test code is now much cleaner.

[kenjis]

@markconnellypro Thank you!