mysql index

Index: a sorted data, the index records the one-to-one correspondence between the position where the index is added and each row of records in the data in the data table.
An index is like a table of contents in a dictionary.

The way mysql traverses data:
Sequential traversal: the query will traverse the data in the database
Index traversal: find the appropriate index, and then locate the data of the corresponding row in the database according to the index, improving the data query ability

Indexing advantages and disadvantages:

Benefits

• All fields can be indexed
• You can add an index to one or more columns in the table

Disadvantages

• The index needs to occupy a certain position, and the data update also requires internal maintenance of the index within mysql

The principle of mysql index creation

• The smaller the data the better, the less memory it takes up
• Simple data types are best
• Try not to create indexes on null values, null values ​​will make index calculation more difficult

mysql data index adds an index to the primary key or foreign key in the data. There is a certain amount of data in the table. This field is mostly used for data retrieval conditions, and this field is used for grouping and sorting.

Type of index

Unique, fulltext, spatial

Index Creation

alter table tableName add index indexName(columnName)