How to view the index information of MySQL tables?

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In the previous article 《MySQL Index in 》 in , We introduced MySQL All the indexes of .

today , Let's learn another command ： show index, View all index information of the table ：

show index from your_tablename;

Through execution show index command , You can get the following results ：

The meaning of each column is as follows ：

1. Table： The name of the table where the index is located ;

2. Non_unique：0 Indicates that the index is unique ,1 Indicates that the index is not unique ;

3. Key_name： Name of index ;

4. Seq_in_index： The position of the index column in the index , For composite indexes , This field is important , You can see 《MySQL  Index in 》;

5. Column_name： The name of the index column ;

6. Collation： How the values of index columns are stored in the index .A Indicates that there is a sort ,B+ The tree index uses this method ;NULL Indicates disordered ,Heap The index uses this method ;

7. Cardinality： The number of all values in the index column after de duplication . The closer the value is divided by the number of rows in the table 1 The better , If it's very small , You need to consider whether you can delete the index ;

8. Sub_part： The number N Indicates that only the first... Of the column N Characters to index ;NULL Represents the value of the entire index column ;

9. Packed： Is the keyword compressed ,NULL No compression ;

10. Null： Whether the index column can be empty

11. Index_type： Index type ,BTREE Express B+ Tree index ;

12. Comment： notes ;

13. Index_comment： notes ;

among , We need to pay special attention   Cardinality  value , If the value is much smaller than the number of rows in the table , Then we need to consider whether we can delete the index .

Develop small knowledge every day , Did you quit today ？