Summary: in this tutorial, you will learn how to query index information from a table by using the MySQL 0 command. Introduction to MySQL SHOW INDEXES FROM table_name IN database_name; Code language: SQL (Structured Query Language) (sql)0 commandTo query the index information of a table, you use the 0 statement as follows:
To get the index of a table, you specify the table name after the 3 keyword. The statement will return the index information associated with the table in the current database. You can specify the database name if you are not connected to any database or you want to get the index information of a table in a different database:
The following query is similar to the one above:
Note that 4 and 5 are the synonyms of the 6, 7 is the synonym of the 3, therefore, you can use these synonyms in the 0 column instead. For example:
Or
The 0 returns the following information: tableThe name of the table non_unique1 if the index can contain duplicates, 0 if it cannot. key_nameThe name of the index. The primary key index always has the name of 1. seq_in_indexThe column sequence number in the index. The first column sequence number starts from 1. column_nameThe column name collationCollation represents how the column is sorted in the index. 2 means ascending, 3 means descending, or 4 means not sorted. cardinalityThe cardinality returns an estimated number of unique values in the index. Note that the higher the cardinality, the greater the chance that the query optimizer uses the index for lookups. sub_partThe index prefix. It is null if the entire column is indexed. Otherwise, it shows the number of indexed characters in case the column is partially indexed. packedindicates how the key is packed; NUL if it is not. null5 if the column may contain NULL values and blank if it does not. index_typerepresents the index method used such as 6, 7, 8, or 9. commentThe information about the index not described in its own column. index_commentshows the comment for the index specified when you create the index with the 0 attribute. visibleWhether the index is visible or invisible to the query optimizer or not; 5 if it is, 2 if not. expressionIf the index uses an expression rather than column or column prefix value, the expression indicates the expression for the key part and also the 3 column is NULL. Filter index informationTo filter index information, you use a 4 clause as follows:
You can use any information returned by the 0 statement to filter the index information. For example, the following statement returns only the invisible indexes of a table:
MySQL SHOW INDEXES FROM table_name IN database_name; (adsbygoogle = window.adsbygoogle || []).push({}); Code language: SQL (Structured Query Language) (sql)0 examplesWe will create a new table named 7 to demonstrate the 0 command:
The following command returns all index information from the 7 table:
The output is: To get the invisible indexes of the 7 table, you add a 4 clause as follows:
Here is the output: In this tutorial, you have learned how to use the MySQL 0 statement to get the index information of a table. What is the list of keys in MySQL?The 5 keys supported by MySQL are Primary Key, Unique Key, Candidate Key, Foreign Key, and Super Key. You learned how to create a table to define and also how to alter the table for primary and unique keys.
How to list all foreign keys in MySQL?To see all FKs in your table: USE '<yourschema>'; SELECT i. TABLE_NAME, i. CONSTRAINT_TYPE, i. CONSTRAINT_NAME, k. ... . To see all the tables and FKs in your schema: USE '<yourschema>'; SELECT i. TABLE_NAME, i. CONSTRAINT_TYPE, i. ... . To see all the FKs in your database: SELECT i. TABLE_SCHEMA, i. TABLE_NAME, i.. How to get list of indexes in MySQL?To see indexes for all tables within a specific schema you can use the STATISTICS table from INFORMATION_SCHEMA: SELECT DISTINCT TABLE_NAME, INDEX_NAME FROM INFORMATION_SCHEMA. STATISTICS WHERE TABLE_SCHEMA = 'your_schema'; Removing the where clause will show you all indexes in all schemas.
How to show primary key in MySQL?MySQL primary key is a single or combination of the field, which is used to identify each record in a table uniquely. If the column contains primary key constraints, then it cannot be null or empty.. CREATE TABLE table_name(. col1 datatype PRIMARY KEY,. col2 datatype,. |