Detailed CAS Principle
An index is a data structure that stores and sorts the values of one or more columns in a database table. It speeds up the search by reducing the number of records that need to be queried in a table. If there is no index, the database will have to perform Full table scan. The index is equivalent to the table of contents in the book, you can quickly find the content you need according to the page number on the table of contents, and improve the query speed.
By creating a unique index, the uniqueness of each row of data in the database table can be guaranteed. It can greatly speed up the data retrieval speed, avoid the data scanning of the whole table, and greatly reduce the number of matching rows traversed. This is also the main reason for creating an index. Can speed up the connection between the table and the table, especially in the realization of the referential integrity of the data is particularly meaningful. When using grouping and sorting clauses for data retrieval, the time for grouping and sorting in the query can be significantly reduced. By using the index, you can use the optimization hider in the query process to improve the performance of the system.
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