Fix #715 by removing subqueries without using regex

[dregad]

Alternative to #718

[dregad]

@mnewnham as mentioned in #718 (comment), it would be nice if you could take a look at this.

[mnewnham]

This seems all good. I was unable to break it with

• Subselects within the 'select from'
• Subselects within the 'where'
• Unmatched parentheses inside strings within the statements

[dregad]

Great, thanks for testing.

[Mike-Benoit]

While I haven't tested this yet, I disagree with removing the _ADODB_COUNT functionally to override the built-in removal of sub-selects. Without a full SQL parser (which will never happen of course), I fail to see how we can handle every possible SQL query that anyone could ever possibly write across all drivers. It seems like pretty cheap insurance to keep around, and even a potential optimization for queries that may be executed often too.

Based on a very quick read of the code, it would appear that the following real-world query (where _ADODB_COUNT is currently used) could possibly fail:

select
_ADODB_COUNT
a.*,
(
CASE WHEN EXISTS
( select 1 from table1 as y where y.accrual_policy_account_id = a.id and y.deleted = 0)
THEN 1
ELSE
CASE WHEN EXISTS
( select 1 from table2 as z where z.accrual_policy_account_id = a.id and z.deleted = 0)
THEN 1
ELSE 0
END
END
) as in_use
_ADODB_COUNT
FROM table3 as a ...;

[dregad]

@Mike-Benoit given the above SQL statement (with or without the _ADODB_COUNT markers), the new parser code in _adodb_getcount() correctly transforms it to SELECT COUNT(*) FROM table3 as a, which is the expected result.