Question

I have a table with three numbers in each record, a minimum, a maximum, and an observed value. I would like to estimate an interpolation that predicts the observed value given minimum and maximum values. To do this, I would like to calculate an average and a standard deviation for the slope and intercept for each record. My understanding is that the STDDEV and AVG functions apply only to queries that have a GROUP BY clause. Mine table doesn’t have anything that I can group by, unless I do something stupid like group by whether the record id is odd or even. Is there a way to compute these kinds of descriptive statistics using MySQL?

Answer 1

You do not have to use GROUP BY to use AVG and STDDEV as the following example shows:

mysql> select * from test;
+------+------+----------+
| min  | max  | observed |
+------+------+----------+
|    1 |   10 |        2 |
|    2 |   20 |        4 |
+------+------+----------+


mysql> SELECT AVG(observed) FROM test;
+---------------+
| AVG(observed) |
+---------------+
|        3.0000 |
+---------------+
1 row in set (0.00 sec)


mysql> SELECT STDDEV(observed) FROM test;
+------------------+
| STDDEV(observed) |
+------------------+
|           1.0000 |
+------------------+
1 row in set (0.00 sec)