SQL Indexes Explained: What is Index Selectivity?
In this short sql tutorial we'll walk you through sql index selectivity.
In the database world, SQL index selectivity is the number of distinct values in a table divided by the total number of records. SQL index selectivity defines how a SQL database index helps the SQL database narrow the search for values.
To calculate SQL index selectivity, divide the distinct values in a table by the total number of records. An ideal SQL index selectivity is a value of 1. The closer to 1 the value is, the better the index selectivity becomes.
Below you can find a couple of sql interview questions and answers - make sure to glance through them before attending your next sql interview!
Q: What types of SQL indexes exist?
A: There are B-Tree indexes, R-Tree indexes, hash indexes, covering indexes, clustered indexes, multicolumn or composite SQL indexes, and prefix indexes.
Q: What is the most popular type of a mysql index?
A: A B-tree sql index is the most popular type of a mysql index.
Q: How to protect against SQL injection?
A: Don't pass user input into a SQL query. You really don't need to pass a mysql advanced tutorial to know this - it's that simple!
Q: What is the file to adjust mysql server configuration?
A: The mysql my.cnf file on Linux or the mysql my.ini file on Windows is what you should look into. If needed, we'll make a separate mysql tutorial for beginners on how it works. A mysql tutorial covering which storage engine - myisam vs innodb - to choose is available here: • MySQL MyISAM vs. InnoDB: Which One to...
Q: Is there a sql full course or any mysql tutorial that would cover mysql storage engines in more detail in all complex aspects?
A: Not that we know of, but if needed, we'll make a sql course talking about everything: sql basics, sql queries, sql vs nosql, sql for data analysis, etc.
Q: Is there a big data tutorial for those looking to work with big data on mysql server?
A: Yes, it's available here: • Big Data Tutorial: MySQL Edition (Big...
Q: I've heard that MyISAM performs row level locking?
A: No, that's a common misconception.
Q: MyISAM vs InnoDB performance - which one is better and why?
A: InnoDB - all of the features that were available in MyISAM are now available in InnoDB.
Enjoy!
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