PRAGMA index_xinfo is a command in SQLite that provides detailed information about an index within a database table. SQLite is a lightweight, self-contained, and serverless relational database management system (RDBMS) that is commonly used in various applications and embedded systems. The PRAGMA index_xinfo command is a powerful tool for developers and database administrators to gain insights into the structure and statistics of an index.
Here is an overview of the key aspects of PRAGMA index_xinfo:
Syntax
The syntax for using PRAGMA index_xinfo is as follows:
PRAGMA index_xinfo(index_name);
Here, index_name is the name of the index you want to retrieve information about.
Purpose
The primary purpose of PRAGMA index_xinfo is to provide metadata about an index, helping users understand how the index is structured and how it affects query performance.
Information Provided
When you execute PRAGMA index_xinfo, you will receive a result set with the following columns:
Seqno: A sequence number that indicates the position of the indexed column within the index. It starts from 0 and increases by 1 for each indexed column in the order they appear in the index.
CID: The column ID of the indexed column. This corresponds to the ordinal position of the indexed column within the table’s schema.
Name: The name of the indexed column.
CollSeq: The collation sequence used for the indexed column, which determines how the values are compared for sorting and searching.
Key: An indicator of whether the indexed column is part of the primary key or not. It is 1 for columns in the primary key and 0 otherwise.
Use Cases
PRAGMA index_xinfo is especially useful when you need to optimize query performance. By examining the information provided by this pragma, you can understand which columns are indexed, their order within the index, and their collation sequences. This knowledge can help you make informed decisions about query optimization, such as selecting the right index for a query or determining if a composite index is appropriately ordered.
Example
Here’s an example of how you might use PRAGMA index_xinfo:
PRAGMA index_xinfo(my_index);
This query would return information about the my_index index, including the sequence numbers, column IDs, names, collation sequences, and key indicators for the indexed columns.
In summary, PRAGMA index_xinfo is a valuable tool for examining the structure of indexes in an SQLite database. It provides essential details about the indexed columns, their order, and collation sequences, which can be instrumental in optimizing database queries and improving overall performance.