Mysql steps to create bitmap index

Steps: 1. Confirm the columns suitable for establishing a bitmap index; 2. Use the CREATE INDEX statement to create a bitmap index; 3. Use a bitmap index, etc.

MySQL is a commonly used relational database management system that provides a variety of index types to improve query efficiency. Among them, bitmap index is a special index type suitable for columns with low cardinality. In this article, I will explain how to build a bitmap index in MySQL.

Bitmap index is a binary bit-based index that uses a bitmap to represent whether each index key value exists in the index. Graph indexes are useful when there are only a few distinct values ​​in a column, such as gender, status, etc. Compared with B-tree indexes, bitmap indexes have certain advantages in terms of storage space and query performance.

In MySQL, to establish a bitmap index, the following conditions need to be met:

1. The cardinality of the column is low: Bitmap indexes are suitable for low cardinality (Cardinality) columns, that is, columns with fewer distinct values. For example, the gender column has only two values ​​(male, female), and the status column has only several different values ​​(such as 1, 2, 3, etc.).

2. Data type of column: Bitmap index can only be used for integer types (including integer and enumeration types). MySQL does not support bitmap indexing on string type columns.

3. Column selectivity: The effect of a bitmap index depends on the selectivity of the column, that is, the distribution of different values ​​in the column. A bitmap index may work better if the different values ​​in the column are more evenly distributed.

The following are the steps to create a bitmap index in MySQL:

1. Confirm the columns suitable for establishing a bitmap index: according to the cardinality of the column, Conditions such as data type and selectivity determine which columns are suitable for establishing a bitmap index.

2. Create a bitmap index: Use the CREATE INDEX statement to create a bitmap index. For example, assuming we want to create a bitmap index for the gender column named gender, we can use the following statement:

   CREATE BITMAP INDEX idx_gender ON table_name (gender);

   This will create a bitmap index named idx_gender on the gender column of the table_name table.

3. Use bitmap index: When querying, MySQL will automatically choose whether to use a bitmap index. You can use the EXPLAIN statement to see whether the query plan uses bitmap indexes.

   For example, assuming we want to query records with male gender, we can use the following statement:

   SELECT * FROM table_name WHERE gender = '男';

   If the bitmap index is correctly selected and used, query performance should be improved.

It should be noted that bitmap indexes are not suitable for situations where the column cardinality is high, because bitmap indexes require a large amount of storage space. In addition, bitmap indexes only apply to equality queries, not range queries. If you need to perform range queries, you still need to use a B-tree index or other suitable index type.

To summarize, the steps to create a bitmap index in MySQL include determining the columns suitable for establishing a bitmap index, creating a bitmap index, and using the bitmap index in queries. Bitmap indexes are suitable for lower cardinality, integer type columns, and work better with better selectivity. However, it should be noted that bitmap indexes are not suitable for situations where the cardinality is high or range queries are required.

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