Project query time off data discovery query time is very long. No doubt take the index time, so explain what
EXPLAIN select * from t_order where created_at>'2015-01-01 00:00:00' and created_at<'2017-01-01 00:00:00'
Resolution:
id：
Expressed order of execution, the id values are the same, the execution order is from top to bottom, the id values are different, the larger the value of id, higher priority, the first execution
select_type:
1, SIMPLE said they did not contain sub-queries and union
2, if the query contains a subquery, the outermost query is marked as: PRIMARY
3, included in the select list or where the sub-queries, they are marked: SUBQUERY
4, sub-queries from would mark: DERIVED
5, selcect result is out of the union flag is: UNION RESULT
type:
He expressed the need to find the type of access line
ALL，index，range，ref，eq_ref，const，system，NULL
Performance from worst to best
key:
Indicate which index to use
From the screenshot above to see did not go create_at index.
Information found on the Internet:
When the index table being queried, the best use of the index, unless the optimizer uses a full table scan is more effective. Optimization best optimization index sake check out the table exceeds 30% of the data depends on the use of table scan data.
The optimizer is more complex, which is estimated based on other factors, in Table size, number of rows and the I / O block size.
I found the reason:
the data using the count of the entire table, and conditions have been found more than 30% ,, so ineffective. When indexing, to be established according to the column base. Column cardinality column different data = / divided by the total data. The closer to 1 indicates
the less duplication, more suitable for indexing.
solve:
According to the above theory, the scope of time off query by order number. Differentiating the time since the order number, and a column base = 1;