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:
- SHOW INDEX FROM table_name FROM db_name;
- SHOW INDEX FROM db_name. table_name;
- SELECT DISTINCT TABLE_NAME, INDEX_NAME FROM INFORMATION_SCHEMA. STATISTICS WHERE TABLE_SCHEMA = `schema_name`;
- 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.
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.