Advantages and disadvantages of MySQL 4 index

Why do you create an index? This is because creating an index can greatly improve the performance of the system.
First, by creating a unique index, you can guarantee the uniqueness of each row of data in a database table.
Second, it can greatly speed up the retrieval of data, which is the main reason for creating indexes.
Thirdly, the connection between tables and tables can be accelerated, particularly in terms of achieving referential integrity of the data.
Finally, when using grouping and sorting clauses for data retrieval, you can also significantly reduce the time to group and sort in queries.

By using the index, we can improve the performance of the system by using the optimized hidden device in the process of querying.

Perhaps someone will ask: there are so many advantages to adding indexes, why not create an index for each column in the table? Although this kind of thought has its rationality, but also has its one-sidedness. Although indexes have many advantages, it is very unwise to add indexes to each column in a table. This is because there is a lot of downside to increasing the index.

First, it takes time to create indexes and maintain indexes, and this time increases as the amount of data increases.
Second, the index needs to occupy the physical space, in addition to the data table to occupy the data space, each index also occupies a certain amount of physical space, if you want to establish a clustered index, then the space will be larger.
Thirdly, when the data in the table is added, deleted and modified, the index should be maintained dynamically, thus reducing the maintenance speed of the data.

Indexes are built on top of some columns in a database table. Therefore, when you create an index, you should carefully consider which columns you can create an index on, and on which columns you cannot create an index.

Advantages and disadvantages of MySQL 4 index