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Re: Strange performance results with JOIN/COUNT
Posted by: Tomas Pluskal
Date: February 09, 2012 03:13AM

Sure, here you go:


mysql> explain extended SELECT msruns.description, COUNT(msrun_peaks.id) AS peaks_count FROM msruns LEFT JOIN msrun_peaks USING (msrun_id) JOIN samples USING (sample_id) GROUP BY msrun_id ORDER BY msruns.id;
+----+-------------+-------------+-------+--------------------+--------------------+---------+-----------------------------------+------+----------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------------+-------+--------------------+--------------------+---------+-----------------------------------+------+----------+----------------------------------------------+
| 1 | SIMPLE | samples | index | sample_id | sample_id | 92 | NULL | 329 | 100.00 | Using index; Using temporary; Using filesort |
| 1 | SIMPLE | msruns | ref | msruns_ibfk_1 | msruns_ibfk_1 | 92 | metabolometomas.samples.sample_id | 1 | 100.00 | |
| 1 | SIMPLE | msrun_peaks | ref | msrun_peaks_ibfk_1 | msrun_peaks_ibfk_1 | 92 | metabolometomas.msruns.msrun_id | 708 | 100.00 | Using index |
+----+-------------+-------------+-------+--------------------+--------------------+---------+-----------------------------------+------+----------+----------------------------------------------+
3 rows in set, 1 warning (0.00 sec)

mysql> explain extended SELECT msruns.msrun_id, COUNT(msrun_peaks.id) AS peaks_count FROM msruns LEFT JOIN msrun_peaks USING (msrun_id) JOIN samples USING (sample_id) GROUP BY msrun_id ORDER BY msruns.id;
+----+-------------+-------------+-------+--------------------+--------------------+---------+-----------------------------------+------+----------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------------+-------+--------------------+--------------------+---------+-----------------------------------+------+----------+----------------------------------------------+
| 1 | SIMPLE | samples | index | sample_id | sample_id | 92 | NULL | 329 | 100.00 | Using index; Using temporary; Using filesort |
| 1 | SIMPLE | msruns | ref | msruns_ibfk_1 | msruns_ibfk_1 | 92 | metabolometomas.samples.sample_id | 1 | 100.00 | |
| 1 | SIMPLE | msrun_peaks | ref | msrun_peaks_ibfk_1 | msrun_peaks_ibfk_1 | 92 | metabolometomas.msruns.msrun_id | 708 | 100.00 | Using index |
+----+-------------+-------------+-------+--------------------+--------------------+---------+-----------------------------------+------+----------+----------------------------------------------+
3 rows in set, 1 warning (0.00 sec)

mysql> explain extended SELECT msruns.description, (SELECT COUNT(id) FROM msrun_peaks WHERE msrun_peaks.msrun_id = msruns.msrun_id) AS peaks_count FROM msruns JOIN samples USING (sample_id) ORDER BY msruns.id;
+----+--------------------+-------------+-------+--------------------+--------------------+---------+-----------------------------------+------+----------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+--------------------+-------------+-------+--------------------+--------------------+---------+-----------------------------------+------+----------+----------------------------------------------+
| 1 | PRIMARY | samples | index | sample_id | sample_id | 92 | NULL | 329 | 100.00 | Using index; Using temporary; Using filesort |
| 1 | PRIMARY | msruns | ref | msruns_ibfk_1 | msruns_ibfk_1 | 92 | metabolometomas.samples.sample_id | 1 | 100.00 | |
| 2 | DEPENDENT SUBQUERY | msrun_peaks | ref | msrun_peaks_ibfk_1 | msrun_peaks_ibfk_1 | 92 | metabolometomas.msruns.msrun_id | 708 | 100.00 | Using index |
+----+--------------------+-------------+-------+--------------------+--------------------+---------+-----------------------------------+------+----------+----------------------------------------------+
3 rows in set, 2 warnings (0.00 sec)

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Re: Strange performance results with JOIN/COUNT
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February 09, 2012 03:13AM


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