What is a MySQL index and types of Index ?
A database index is a data structure that improves the speed of data retrieval operations on a database table but the cost of additional writes and storage space to maintain the index data structure. Indexes improve database performance because index speeding up query processing.
- PRIMARY index is called clustered indexes and others indexes are secondary indexes or non-clustered ndexes.
- INSERT, UPDATE and DELETE becomes slower because on each operation the indexes must also be updated.
- SELECT statement is fast
By default, MySQL creates the B-Tree index if you don’t assign the index type.Most MySQL indexes (PRIMARY KEY, UNIQUE, INDEX, and FULLTEXT) are stored in B-trees index type.
- Indexes on spatial data types use R-trees;
- MEMORY tables also support hash indexes;
- InnoDB uses inverted lists for FULLTEXT indexes.
What are the types of indexes in MySQL?
Five Types of Indexes
- PRIMARY KEY (Clustered Index) : When you created any table with a primary key then MySQL automatically created a index called PRIMARY. This index is called the clustered index because the index itself is stored together with the data in the same table so Speeds Up Queries.
- UNIQUE : A unique index is the all values must be unique in a single column.In multi-column unique index the values can be duplicated in a single column, but the combination of column values in each record(row) must be unique.
- INDEX(Ordinary index)
- DESCENDING INDEX (in version 8+ of MySQL)
#create index syntax
CREATE INDEX index_name ON table_name (column_list)
#display all indexes of table
SHOW INDEX FROM table_name;
1- If you do not define a PRIMARY KEY for your table, MySQL locates the first UNIQUE index where all the key columns
are NOT NULL and InnoDB uses it as the clustered index.
2-If you do not define a PRIMARY KEY or UNIQUE index for your table,InnoDB internally generates a hidden clustered index named GEN_CLUST_INDEX on a synthetic column containing row ID values.
Advantages and disadvantages of indexes
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