> trade_time IN ('2012-07-01', '2012-07-02');
represents two distinct points in a continuum of a DATETIME. Perhaps you
should change to DATE. Even then, it would probably be treated as IN, not
RANGE. Perhaps you really want BETWEEN (a "range") instead of IN (a set).
What version are you using? Older version have essentially no optimizations
for IN().
Shrinking the table size may help -- Do you really need BIGINT (8 bytes)
instead of INT UNSIGNED (4 bytes)? DATETIME (8) vs DATE(3). Etc.
If these are stock prices, how can `price` be INT?
> -----Original Message-----
> From: Jeffrey Grollo [mailto:grol...@gmail.com]
> Sent: Tuesday, July 10, 2012 2:50 PM
> To: mysql@lists.mysql.com
> Subject: Composite Index Usage in Joins
>
> Hi,
>
> I'm attempting to optimize a join and am having a difficult time using
> multiple columns from a composite index. The second column of the
> composite key is being used when tested for equality, but not for IN or
> BETWEEN criteria.
>
> As an example, say that I'm searching two tables: portfolio and trades.
> The portfolio table contains a list of security IDs. The trades table
> keeps tracks of the price and time when I've traded securities in my
> portfolio.
> Tables are:
>
> CREATE TABLE portfolio (
> sec_id bigint(20) NOT NULL AUTO_INCREMENT,
> name char(10) NOT NULL,
> PRIMARY KEY (sec_id)
> ) ENGINE=InnoDB ;
>
> CREATE TABLE trades (
> tx_id bigint(20) NOT NULL AUTO_INCREMENT,
> sec_id bigint(20) NOT NULL,
> trade_time datetime NOT NULL,
> price int NOT NULL,
> PRIMARY KEY (tx_id),
> KEY sec_time (sec_id, trade_time)
> ) ENGINE=InnoDB ;
>
> If I query the trades table directly both columns of the composite
> index "sec_time" will be used when I'm using a range criteria on the
> trade_time
> column:
>
>
> mysql> explain select price from trades force index(sec_time)
> -> where sec_id IN (1, 2) and trade_time BETWEEN '2012-07-01' AND
> '2012-07-04';
> +----+-------------+--------+-------+---------------+----------+-------
> --+------+------+-------------+
> | id | select_type | table | type | possible_keys | key |
> key_len |
> ref | rows | Extra |
> +----+-------------+--------+-------+---------------+----------+-------
> --+------+------+-------------+
> | 1 | SIMPLE | trades | range | sec_time | sec_time | 16
> |
> NULL | 2 | Using where |
> +----+-------------+--------+-------+---------------+----------+-------
> --+------+------+-------------+
>
>
> If I introduce a join to retrieve all trades for my portfolio, the
> entire index will continue to be used if I make trade_time a constant:
>
> mysql> explain select price from portfolio p inner join trades t force
> index(sec_time) on p.sec_id = t.sec_id
> -> where trade_time = '2012-07-01';
> +----+-------------+-------+-------+---------------+----------+--------
> -+------------------------+------+-------------+
> | id | select_type | table | type | possible_keys | key | key_len
> |
> ref | rows | Extra |
> +----+-------------+-------+-------+---------------+----------+--------
> -+------------------------+------+-------------+
> | 1 | SIMPLE | p | index | PRIMARY | PRIMARY | 8
> |
> NULL | 1 | Using index |
> | 1 | SIMPLE | t | ref | sec_time | sec_time | 16
> |
> vantage.p.sec_id,const | 1 | |
> +----+-------------+-------+-------+---------------+----------+--------
> -+------------------------+------+-------------+
>
>
> However, if I expand the trade_time search (either using IN or
> BETWEEN), only the sec_id column of the composite query is used:
>
>
> mysql> explain select price from portfolio p inner join trades t force
> index(sec_time) on p.sec_id = t.sec_id
> -> where trade_time IN ('2012-07-01', '2012-07-02');
> +----+-------------+-------+-------+---------------+----------+--------
> -+------------------+------+-------------+
> | id | select_type | table | type | possible_keys | key | key_len
> |
> ref | rows | Extra |
> +----+-------------+-------+-------+---------------+----------+--------
> -+------------------+------+-------------+
> | 1 | SIMPLE | p | index | PRIMARY | PRIMARY | 8
> |
> NULL | 1 | Using index |
> | 1 | SIMPLE | t | ref | sec_time | sec_time | 8
> |
> vantage.p.sec_id | 1 | Using where |
> +----+-------------+-------+-------+---------------+----------+--------
> -+------------------+------+-------------+
>
>
> My expectation is that MySQL would be able to use both columns of the
> sec_time index, but I've been unable to find either confirmation of
> refutation of that assumption. If MySQL cannot optimize a join in this
> case, is there another approach to optimizing this query that I should
> pursue? Essentially, my trades table may contain many historical
> records and pulling the entire history of trades for each security
> would produce a much larger result set than would be retrieved if the
> trade_time criteria was applied in the index reference.
>
> I'm using MySQL 5.5.11.
>
> Thanks for any guidance,
> Jeff
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