composite-index

Imagine you have a primary composite index of last_name,first_name . Then you performed a search of WHERE first_name LIKE 'joh%' AND last_name LIKE 'smi%' . Does the wildcard used in the last_name condition mean that the first_name condition will not be used in further helping MySQL find indexes? In other words, by putting a wildcard on the last_name condition MySQL will only do a partial index lookup (and ignores conditions given in the columns that are to the right of last_name)? Further clarification of what I'm asking Example-1: Primary key is last_name, first_name . Example-2: Primary key

Are there any differences between following two indexes? IDX_IndexTables_1 IDX_IndexTables_2 If there are any, what are the differences? create table IndexTables ( id int identity(1, 1) primary key, val1 nvarchar(100), val2 nvarchar(100), ) create index IDX_IndexTables_1 on IndexTables (val1, val2) GO create index IDX_IndexTables_2 on IndexTables (val2, val1) GO Yes. There is a difference. The composite index IDX_IndexTables_1 can be used for any query where the val1 column is used in the where clause. The composite index IDX_IndexTables_2 can be used for any query where the val2 column is

I am looking into adding a composite index to a table in a MYSQL database which will likely be several million rows in size. The composite will be comprised of two varchar columns as well as three int columns. My question is as stated in the title: is there an optimal order in which to create this composite index? For instance, one of the int rows will likely only have 6 possible values, would it better for that column to be closer to the front of the index definition? Likewise, one of the varchar columns will likely have millions of different values, should that be near the front or back of

In the following query SELECT col1,col2 FROM table1 WHERE col3='value1' AND col4='value2' If I have 2 separate indexes one on col3 and the other on col4 , Which one of them will be used in this query ? I read somewhere that for each table in the query only one index is used. Does that mean that there is no way for the query to use both indexes ? Secondly, If I created a composite index using both col3 and col4 together but used only col3 in the WHERE clause will that be worse for the performance? example: SELECT col1,col2 FROM table1 WHERE col3='value1' Lastly, Is it better to just use

When should I use a composite index in a database? What are the performance ramification by using a composite index)? Why should I use use a composite index? For example, I have a homes table: CREATE TABLE IF NOT EXISTS `homes` ( `home_id` int(10) unsigned NOT NULL auto_increment, `sqft` smallint(5) unsigned NOT NULL, `year_built` smallint(5) unsigned NOT NULL, `geolat` decimal(10,6) default NULL, `geolng` decimal(10,6) default NULL, PRIMARY KEY (`home_id`), KEY `geolat` (`geolat`), KEY `geolng` (`geolng`), ) ENGINE=InnoDB ; Does it make sense for me to use a composite index for both geolat