Why is this simple query taking more than 1 second?
I'm not an expert on MySQL, but it looks to me like it's doing a table scan by secid_date, which isn't even in the query at all. And scanning 17M rows is not what you want to be doing unless you really have to.

Check your indexes

mysql&gt; SHOW INDEX FROM financial_key_ratios\G


I would make sure that you have something like

+-----------------------+------------+------------+--------------+---------------+ ... 
| Table                 | Non_unique | Key_name   | Seq_in_index | Column_name   | ... 
+-----------------------+------------+------------+--------------+---------------+ ... 
| financial_key_ratios  |          1 | ...        |            1 | SecurityId    | ... 


and if possible

| financial_key_ratios  |          1 | ...        |            2 | DateModified  | ... 


If you aren't indexing on at least SecurityId, you can add it with

CREATE INDEX IdxSecurityId ON financial_key_ratios (SecurityId)


You can take it a step further and include DateModified

CREATE INDEX IdxSecurityId_DateModified ON financial_key_ratios (SecurityId, DateModified)