Hey everyone,
I have a question about the speed of selecting distinct values on an
indexed column. I have a table with a five column primary key and 3,215,540
records. I want to select all of the distinct values of the first column in
the primary key. This column only has 549 distinct values. To execute this
query takes about a minute and a half on a P4 2.4G. I assume that mysql is
doing a complete table scan thus making the query slow.
My question follows. Shouldn't the distinct values of the first
column in an index be pulled from the index itself instead from the actual
data? Thanks for your insights!
Nathan
show table status;
-------+-------------+------------+----------------+------------------------
---+
| Name | Type | Row_format | Rows | Avg_row_length | Data_length
| Max_data_length | Index_length | Data_free | Auto_increment | Create_time
| Update_time | Check_time | Create_options | Comment |
+------------------------+--------+------------+----------+----------------+
-------------+-----------------+--------------+-----------+----------------+
-------
| PostedZpdi | InnoDB | Dynamic | 3215540 | 678 | 2180988928
| NULL | 530350080 | 0 | NULL | NULL | NULL
| NULL | | InnoDB free: 142368768 kB |
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