Hi I am a newbie to mysql
Here are my questions:
What is the use of Mysql Index key?
Does it make a difference in mysql queries with defining an Index key and without it?
Are all primary keys default Index key?
Thanks a million
1- Defining an index on a column (or set of columns) makes searching on that column (or set) much faster, at the expense of additional disk space.
2- Yes, the difference is that queries using that column will be much faster.
3- Yes, as it's usual to search by the primary key, it makes sense for that column to always be indexed.
Read more on MySQL indexing here .
An index is indeed an additional set of records. Nothing more.
Things that make indexes access faster are:
To know whether or not an index is useful is not so easy to guess (obviously I'm not talking about the primary key) and should be investigated. Here are some counterparts when it might slow down your operations:
Now about your question 'Are all primary keys default Index key?', I must say that it is not like this that the optimizer works. When there are various indexes defined in a table, the more efficient index combination will be compiled with on the fly datas and some other static datas (indexes statistics), in order to reach the best performances. There's no default index per se, every situation leeds to a different result.
Regards.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.