MySQL learning record 07 index (simple understanding)

MySQL Learning record 07 Indexes （ Simple understanding ）

MySQL The official definition of index is ： Indexes (Index) Help MySQL Data structure for efficient data acquisition .
Extract the sentence trunk , We can get the essence of index ： An index is a data structure .《 Article, understand MySQL Indexes （ clear ）》

7.1 Classification of indexes

• General index (KEY/INDEX)
  default
• unique index (UNIQUE KEY)
  Avoid duplicate columns , The unique index can be repeated , Multiple columns can be identified as unique indexes
• primary key (PRIMARY KEY)
  Unique identification , The primary key cannot be repeated , There can only be one column as the primary key
• Full-text index (FullText)
  Only under the specific database engine
  Quickly locate data

7.2 Indexing principles

• More indexes is not better
• Don't index frequently changing data
• A table with a small amount of data does not need to be indexed
• The index is usually added to the fields commonly used for query