Index in MySQL show index from XXX the meaning of each parameter

1. Introduce mysql in index（ Index the meaning of each parameter ）
2. sentence

show index from tb_user

The corresponding result

3. Let's explain the meaning of each parameter of the index in this table
1.Table: Table name

2.Non_unique: If the index cannot contain duplicate values, then 0, If yes, it is 1. That's what we usually call the only index .

3.Key_name The index name , If the name is the same, it indicates that it is the same index , Instead of repeating , For example, the fourth 、 Five pieces of data , The index names are name, It's actually a joint index .

4.Seq_in_index Column sequence number in index , from 1 Start . Four in the above figure 、 Five pieces of data ,Seq_in_index One is 1 One is 2, Is to indicate the order in the joint index , We can infer the order of indexes in the joint index .

5.Column_name The column name of the index .

6.Collation This refers to how columns are stored in the index , It probably means character order .

7.Cardinality Cardinality means , An estimate of the number of unique values in an index . We know that the fewer duplicate values of a field, the more suitable for indexing , So we are generally based on Cardinality To determine whether the index is highly selective , If this value is very small , Then you need to re evaluate whether this field is suitable for indexing .

8.Sub_part Pre index means , If the column is only partially indexed , Is the number of characters indexed . If the entire column is indexed , Then for NULL.

9.Packed Indicates how keywords are compressed . If it's not compressed , Then for NULL. Compression generally includes compressed transmission protocol 、 Compressed column solution and compressed table solution .

10.Null If the column contains NULL, It contains YES.

11.Index_type Represents the index type ,Mysql At present, there are mainly the following index types ：FULLTEXT,HASH,BTREE,RTREE.

12.Comment Index_comment The meaning of the note .

Sum up , This article mainly discusses MySQL SHOW INDEX Use of commands , It is recommended that you run the code below in person .

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