title: mySQL returns empty even though it shouldn't?
body: <p>am a total mySQL newbie, but I have no idea how to search for the answer to this, so that's why I'm bringing it here:</p>
  
  <pre><code>            DESCRIBE rParam;
              +----------------+---------------+------+-----+---------+-------+
              | Field          | Type          | Null | Key | Default | Extra |
              +----------------+---------------+------+-----+---------+-------+
              | p              | float         | YES  |     | NULL    |       |
              | d              | float         | YES  |     | NULL    |       |
              | LTP            | float         | YES  |     | NULL    |       |
              | LTD            | float         | YES  |     | NULL    |       |
              | alpha          | float         | YES  |     | NULL    |       |
              | N              | smallint(6)   | YES  |     | NULL    |       |
              | g              | float         | YES  |     | NULL    |       |
              | a              | float         | YES  |     | NULL    |       |
              | seed           | float         | YES  |     | NULL    |       |
              | startingWeight | float         | YES  |     | NULL    |       |
              | path           | varchar(1000) | YES  | UNI | NULL    |       |
              | type           | varchar(100)  | YES  |     | NULL    |       |
              +----------------+---------------+------+-----+---------+-------+
              12 rows in set (0.00 sec)
  
  
              SELECT p FROM rParam GROUP BY p;
  
              +--------+
              | p      |
              +--------+
              |      0 |
              |  0.001 |
              |  0.002 |
              |  0.003 |
              |  0.004 |
              |  0.005 |
              | 0.0075 |
              |  0.008 |
              |   0.01 |
              |  0.012 |
              | 0.0125 |
              |  0.014 |
              |  0.015 |
              |   0.02 |
              |  0.025 |
              |   0.03 |
              |  0.035 |
              |   0.04 |
              |   0.05 |
              |    0.1 |
              |    0.2 |
              |    0.3 |
              |    0.4 |
              |    0.5 |
              |    0.6 |
              |    0.7 |
              +--------+
              26 rows in set (0.00 sec)
  </code></pre>
  
  <p>I can get the results for one type of query:</p>
  
  <pre><code>            SELECT p FROM rParam WHERE p=0.5 GROUP BY p;
              +------+
              | p    |
              +------+
              |  0.5 |
              +------+
              1 row in set (0.00 sec)
  </code></pre>
  
  <p>However, changing the p-value that I'm asking for:</p>
  
  <pre><code>            SELECT p FROM rParam WHERE p=0.6 GROUP BY p;
              Empty set (0.00 sec)
  </code></pre>
  
  <p>but we can clearly see from the first output that there are rows for which p=0.6? This is a problem for most of the p-values - why does mySQL return the empty set?</p>