Not grouped by the title column. The title columns are aggregated via
a concatenation operation: string_agg()
Does that mean that the select clause is interpreted before the having
clause?
To be more specific what does GROUP BY() mean?
() is the empty GROUPING SET. The subtle difference between GROUP BY
() and no GROUP BY / HAVING at all is the fact that with GROUP BY (),
you can get zero rows. Without GROUP BY / HAVING, you will get at
least one row.
The SQL Server documentation explains this very nicely with examples:
https://technet.microsoft.com/en-us/library/bb522495(v=sql.105).aspx
<https://technet.microsoft.com/en-us/library/bb522495%28v=sql.105%29.aspx>
I read the page but to me it seemed a little difficult to grasp.
Let's go over an example.
TABLE: T1
*-------*------*
| TITLE | YEAR |
*=======*======*
| abcdd | 1973 |
*-------*------*
| abxyz | 1973 |
*-------*------*
| ddefg | 1976 |
*-------*------*
SELECT STRING_AGG(TITLE, ', ')
FROM T1
WHERE TITLE LIKE 'ab%'
HAVING COUNT(*) > 1
According to you this returns: "abcdd, abxyz"
because first 2 rows are filtered by the where clause from T1.
Then that result is grouped using the aggregate operators in select clause.
And finally having clause filters out those aggregated rows that do not
satify
having clauses condition applied to groupings before aggregation.
Is this interpretation correct?
Questions that arises immediately is that what if GROUP BY clause does
exist.
Do we aggregate first using aggregate operators in select or group bu
clause?
When is the having in that case applied?
Is the evaluation order (when order by exists)
1) select, group by, having
2) group by, select, having
3) group by, having, select
?
- Rami
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