Advantages and disadvantages of MySQL indexes and guidelines for creating indexes

1. Why create an index? (Advantages)

This is because creating indexes can greatly improve system performance.

• First, by creating a unique index, the uniqueness of each row of data in the database table can be guaranteed.
• Second, it can greatly speed up data retrieval, which is also the main reason for creating an index.
• Third, it can speed up the connection between tables, which is especially meaningful in achieving the referential integrity of data.
• Fourth, when using grouping and sorting clauses for data retrieval, the time for grouping and sorting in the query can also be significantly reduced.
• Fifth, by using indexes, you can use optimized hiders during the query process to improve system performance.

2. Disadvantages of establishing directional indexes

Some people may ask: Since adding indexes has so many advantages, why not create an index for every column in the table? This idea is certainly reasonable, but it is also one-sided. Although indexes have many advantages, it is unwise to add an index to every column in a table. This is because adding indexes also has many disadvantages.

• First, creating and maintaining indexes takes time, and this time increases as the amount of data increases.
• Second, indexes require physical space. In addition to the data space occupied by the data table, each index also occupies a certain amount of physical space. If you want to create a clustered index, the space required will be even greater.
• Third, when adding, deleting, and modifying data in the table, the index must also be maintained dynamically, which reduces the speed of data maintenance.

3. Guidelines for designing indexes

Indexes are created on certain columns in a database table. Therefore, when creating an index, you should carefully consider which columns can be indexed and which columns cannot be indexed.

Generally speaking, you should create indexes on these columns.

• First, it can speed up the search on columns that are frequently searched.
• Second, on the column that serves as the primary key, enforce the uniqueness of the column and organize the data structure in the table;
• Third, on columns that are often used in connections, which are mainly foreign keys, the connection speed can be accelerated;
• Fourth, create an index on the column that often needs to be searched by range, because the index is already sorted and the specified range is continuous;
• Fifth, create indexes on columns that often need to be sorted. Since the index is already sorted, queries can use the sorting of the index to speed up sorting query time.
• Sixth, create indexes on columns that are frequently used in the WHERE clause to speed up the judgment of conditions.

Likewise, there are some columns for which indexes should not be created. Generally speaking, columns that should not be indexed have the following characteristics:

• First, you should not create indexes on columns that are rarely used or referenced in queries. This is because, since these columns are rarely used, indexing them or not will not improve query speed. On the contrary, the addition of indexes reduces the system maintenance speed and increases the space requirements.
• Second, you should not add indexes to columns that have very few data values. This is because these columns have very few values, such as the gender column of the personnel table. In the query result, the data rows in the result set account for a large proportion of the data rows in the table, that is, the proportion of data rows that need to be searched in the table is very large. Adding indexes does not significantly speed up retrieval.
• Third, indexes should not be added to columns defined as text, image, and bit data types. This is because the data volume of these columns is either quite large or has very few values.
• Fourth, when the modification performance is much greater than the retrieval performance, you should not create an index. This is because modification performance and retrieval performance are contradictory to each other. When adding indexes, retrieval performance will be improved, but modification performance will be reduced. When you reduce the number of indexes, modification performance improves and retrieval performance decreases. Therefore, when modification performance is much greater than retrieval performance, indexes should not be created.

The above is the detailed content of the advantages and disadvantages of MySQL indexes and the criteria for creating indexes. For more information about MySQL indexes, please pay attention to other related articles on 123WORDPRESS.COM!