What does "index" mean?

Refers to the information extracted from the main contents or titles of books and periodicals, indicating the source and page number, and arranged in a certain order for people to consult.

Pronunciation: suǒ yǐn

function

Establishing indexes in the database system mainly has the following functions:

(1) Get data quickly;

(2) Ensure the uniqueness of data records;

(3) Realizing referential integrity between tables;

(4) When using ORDER by and group by clauses for data retrieval, using indexes can reduce the time of sorting and grouping.

superiority

1. Greatly speeds up data retrieval;

2. Create a unique index to ensure the uniqueness of each row of data in the database table;

3. Accelerate the connection between instruments;

4. When using grouping and sorting clauses for data retrieval, the time of grouping and sorting in the query can be significantly reduced.

disadvantaged

The 1. index takes up physical space.

2. When adding, deleting and modifying the data in the table, the index should also be maintained dynamically, which reduces the speed of data maintenance.