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MySQL learning record 07 index (simple understanding)
2022-07-06 08:26:00 【Jatine】
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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
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