Can you use an index in MySQL order by column?
However, MySQL cannot use an index for mixed ASC,DESC order by ( SELECT * FROM foo ORDER BY bar ASC, pants DESC ). Sharing your query and CREATE TABLE statement would help us answer your question more specifically. For hints on how to optimize ORDER BY clauses: http://dev.mysql.com/doc/refman/5.1/en/order-by-optimization.html
How to sort values by order in MySQL?
First, sort the result set by the values in the column1 in ascending order. Then, sort the sorted result set by the values in the column2 in descending order. Note that the order of values in the column1 will not change in this step, only the order of values in the column2 changes.
How to use custom order by in MySQL?
MySQL ORDER BY with custom sort order. The ORDER BY clause enables you to define your own custom sort order for the values in a column using the FIELD() function. See the following orders table. For example, if you want to sort the orders based on the following status by the following order: In Process. On Hold.
What does DESC stand for in MySQL ORDER BY clause?
In this syntax, you specify the one or more columns which you want to sort after the ORDER BY clause. The ASC stands for ascending and the DESC stands for descending. You use ASC to sort the result set in ascending order and DESC to sort the result set in descending order. This ORDER BY clause sorts the result set in ascending order:
How to check the Order of columns in an index?
Start with column (s) tested with =, in any order. Then tack on one range column. Swapping the order in the index would have it totally ignore deleted. (There are a lot more rules for ordering the columns.) Thanks for contributing an answer to Stack Overflow!
When to use an index in SQL Server?
SQL Server can use an index for a range scan only if the leftmost column is specified, and then only if the next leftmost column is specified, and so on. If you have an index on (A,B,C) it can be used to range scan for A=@a, for A=@a AND B=@b but not for B=@b, for C=@c norB=@b AND C=@c.
When to use an index on the mostselective column?
With that knowledge in hand you can look at the index definitions again. An index on (MostSelective, SecondMost, Least) will be effective only when MostSelective column is specified. But that being the most selective, the relevance of the inner columns will quickly degrade.