Table structure (search_stats):
+---------+------------+------+-----+---------+----------------+
| Field   | Type       | Null | Key | Default | Extra          |
+---------+------------+------+-----+---------+----------------+
| id      | int(11)    |      | PRI | NULL    | auto_increment |
| PMID    | int(11)    |      | MUL | 0       |                |
| PMkey   | varchar(4) |      | MUL |         |                |
| PMvalue | longtext   |      |     |         |                |
+---------+------------+------+-----+---------+----------------+

Sample data:
+-------+----------+-------+---------+
| id    | PMID     | PMkey | PMvalue |
+-------+----------+-------+---------+
| 27941 |  7321569 | MH    | Female  |
| 27976 |   293324 | MH    | Adult   |
| 27982 |   293324 | MH    | Female  |
| 28039 |  1168727 | MH    | Female  |
| 28164 |  4493249 | MH    | Female  |
| 28165 |  4493249 | AD    | Brazil  |
| 28206 |  5545272 | MH    | Adult   |
| 28214 |  5545272 | MH    | Female  |
| 28252 |  5841289 | MH    | Female  |
+-------+----------+-------+---------+
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