What is possible keys in MySQL?

How many keys are available in MySQL?

Summary. Eight types of key in DBMS are Super, Primary, Candidate, Alternate, Foreign, Compound, Composite, and Surrogate Key. A super key is a group of single or multiple keys which identifies rows in a table. Primary Key never accept null values while a foreign key may accept multiple null values.

How do I show MySQL keys?

To list all indexes of a specific table:

  1. SHOW INDEX FROM table_name FROM db_name;
  2. SHOW INDEX FROM db_name. table_name;
  3. SELECT DISTINCT TABLE_NAME, INDEX_NAME FROM INFORMATION_SCHEMA. STATISTICS WHERE TABLE_SCHEMA = `schema_name`;
  4. SELECT DISTINCT TABLE_NAME, INDEX_NAME FROM INFORMATION_SCHEMA. STATISTICS;

What is multiple key in MySQL?

1 Answer. 1. 0. there can be multiple keys (that is several keys) on a table to speed up different types of queries. Some of the keys can be multiple column keys (composite keys)

How do I find my super key?

We can define a super key as a set of those keys that identify a row or a tuple uniquely. The word super denotes the superiority of a key. Thus, a super key is the superset of a key known as a Candidate key (discussed in the next section). It means a candidate key is obtained from a super key only.

How do I see indexes in MySQL?

To see the index for a specific table use SHOW INDEX: SHOW INDEX FROM yourtable; 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.

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How can I see foreign keys in MySQL?

To see foreign key relationships of a column:

SELECT TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME FROM INFORMATION_SCHEMA. KEY_COLUMN_USAGE WHERE REFERENCED_TABLE_SCHEMA = ‘db_name’ AND REFERENCED_TABLE_NAME = ‘table_name’ AND REFERENCED_COLUMN_NAME = ‘column_name’;

What is explain in MySQL?

The EXPLAIN statement provides information about how MySQL executes statements: EXPLAIN works with SELECT , DELETE , INSERT , REPLACE , and UPDATE statements. … That is, MySQL explains how it would process the statement, including information about how tables are joined and in which order.