Add Support in the "Position" Function

[yuval-illumex]

Add support to the function position as described in the docs

Example:

SELECT POSITION('@' in field)
FROM table

[coveralls]

Pull Request Test Coverage Report for Build 2215898239

• 19 of 20 (95.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 90.38%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser.rs	10	11	90.91%

Totals
Change from base Build 2215333087:	0.01%
Covered Lines:	8023
Relevant Lines:	8877

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💛 - Coveralls

[alamb]

Thanks @yuval-illumex -- Does POSITION('@' in 'foo') parse in sqlparser without changes today? Or is this PR required to parse the expression?

[yuval-illumex]

@alamb Updated the PR, changed the POSITION function to be like any other function (But the parsed response must use a struct for POSITION)

[alamb]

Sorry for the delayed review @yuval-illumex -- I have been quite busy recently.

I didn't appreciate that <expr> IN <expr> was only valid within the context of a POSITION() function. Sorry for my confusion

Can you please change this code so that the POSITION function is handled specially (I realize you did do that initially and I implied you should change)?

Thanks and sorry again.

[yuval-illumex]

@alamb Thanks for the detailed feedback! Missed the bug with IN.
Appreciate new feedback after the fix

[alamb]

Looks good to me -- thank you @yuval-illumex ❤️

[alamb]

I wrote up a small negative case here as well: #469