Multi-column index in MySql: How to build multiple indexes according to business needs

MySql is a popular relational database management system, and multi-column index is a common index type. Unlike single-column indexes, multi-column indexes can improve query performance and efficiency, especially on large data sets.

However, multi-column indexes may also cause performance degradation, because too many indexes may increase the overhead of writing. When designing a multi-column index, you need to select and optimize it based on specific business needs.

The following are some suggestions to help developers build multiple indexes based on business needs.

1. Determine the conditions of the query
   Before building a multi-column index, developers need to clearly understand the conditions of the query. This can be a combination of one or more columns, such as height and weight, age and gender, etc. Only after a clear understanding of the query conditions can you decide which columns need to be indexed.
2. Optimize index order
   Multi-column indexes are usually matched in the order of columns. If a column is known to have better selectivity, you can usually put it earlier in the index. For example, if your query filters based on status and date, you should typically place the status column before the date column because the status column generally has better selectivity.
3. Avoid using large text columns
   Text columns are often very large and very expensive to index and query. If you need to store large amounts of text data, consider using full-text search instead of indexing it in a multi-column index.
4. Optimize index based on data distribution
   As data entries increase, the index may become different. If some columns in an index are distributed unbalancedly, query performance may suffer. When designing a multi-column index, you need to consider the distribution of the data so that the index can be adjusted based on the data distribution.
5. Avoid duplicate indexes
   Multi-column indexes can cover multiple columns, but in some cases it is more efficient for each column to have its own single-column index. This needs to be taken into consideration when designing multi-column indexes to avoid creating redundant indexes unnecessarily.
6. Avoid creating too many indexes
   Although multi-column indexes can improve query performance, creating too many indexes may cause performance degradation. If you have too many indexes, it can affect write performance and make query plans more complex. When designing a multi-column index, you should decide how many indexes to create based on business needs and actual conditions.

In short, when designing a multi-column index, you need to select and optimize it according to specific business needs. Developers need to understand query conditions, data distribution, and index order, and avoid creating redundant or excessive indexes. Through the above techniques and methods, you can better utilize multi-column indexes to improve query performance and efficiency.

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