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Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows.  Five Types of Indexes When you create an index or add one to an existing table, you’ll create it as one of several types of indexes. A unique index is one in which all column values must be unique. In a single column unique index there can be no duplication of values in the column being indexed. In a multi-column unique index the values can be duplicated in a single column, but the combination of column values in each row must be unique. You use a unique index to prevent duplicate values and you often define the index after a table has been created. A primary key is a unique index in which no value can be NULL. Every row must have a value for the column or combination of columns. You would usually define a primary key on the smallest number of columns possible because of this, and most of the time a

1) What are the usages of SQL? To execute queries against a database To retrieve data from a database To inserts records in a database To update records in a database To delete records from a database To create new databases To create new tables in a database To create views in a database 2) Does SQL support programming? No, SQL doesn't have loop or Conditional statement. It is used like commanding language to access databases. 3) What are the subsets of SQL? Data definition language (DDL) - Data definition language(DDL) allows you to CREATE, ALTER and DELETE database objects such as schema, tables, view, sequence etc. Data manipulation language (DML) - Data manipulation language makes user able to access and manipulate data. It is used to perform following operations. Insert data into database Retrieve data from the database Update data in the database Delete data from the database Data control language (DCL) - Data control

The MySQLi functions allow you to access MySQL database servers. Note: The MySQLi extension is designed to work with MySQL version 4.1.13 or newer. Function Description mysqli_affected_rows() Returns the number of affected rows in the previous MySQL operation mysqli_autocommit() Turns on or off auto-committing database modifications mysqli_change_user() Changes the user of the specified database connection mysqli_character_set_name() Returns the default