This doesn't work on non join queries.... example:
SELECT COUNT(1) AS c FROM (SELECT FROM transaction_line WHERE transaction_id = '1') AS original_select

Commenting out the line that resets the the columns fixes this.

Hmm, resetting should reset columns not to empty but to a wildcard I think. I'll look into this.

In addition, I am not sure columns() needs to be reset at all, what do you think about this patch now?

IMO, the columns don't need to be reset... looks good.

Yeah, I've asked in #zftalk.dev, and they agree. If we need to do any kind of performance enhancements (which is basically what resetting columns is), we can do them elsewhere at a different time (perhaps in those vendor specific modules I mentioned).

Thanks, I'll work up unit tests and get this going.

In issue did not reset columns in select query to determine the count of rows in the grouped queries. Here there was a problem in my opinion. The count() method throws an error when original_select will be such:

SELECT *, TRIM(str_column) as str_column FROM table

PDOException: SQLSTATE[42S21]: Column already exists: 1060 Duplicate column name 'str_column'

Query is good work: SELECT *, TRIM(str_column) as str_column FROM table

But query determine the count of rows throws an error:
SELECT COUNT(1) AS "c" FROM ( SELECT *, TRIM(str_column) as str_column FROM table ) AS "original_select"

The error resulted in higher.

I think need to reset columns original_select on '*'.

$select->reset(Select::COLUMNS);
$select->columns(array(Select::SQL_STAR));

So everything will work correctly.

And why delete code which get join information, clear, and repopulate without columns?

If in join uses the same technique ( e.g. TRIM(str_column) as str_column ) appears the same error. For this you need to reset the column in join. Since it was originally.