Mysql key vs index May 20, 2010 · A primary key is a constraint, not an index. Mar 6, 2016 · As per MySql documentation, KEY is normally a synonym for INDEX. 9, “Secondary Indexes and Generated Columns”. On the other hand, an index has a list of keywords, so you'd consult the index and see that storage is mentioned on pages 113-120, 231, and 354. Each InnoDB table has a special index called the clustered index that stores row data. See Section 10. 20. With the InnoDB storage engine, the table data is physically organized to do ultra-fast lookups and sorts based on the primary 1. I would appreciate if someone well-versed in their difference explai I have a table of unique values (domains_unique), with column domain varchar(255), with more than 20 mil records. Its implementation is CREATE INDEX cannot be used to create a PRIMARY KEY; use ALTER TABLE instead. A composite index on (email, user_id) is enough, you don't need a separate index on email only - MySQL can use leftmost parts of a composite index. 4, “Index Hints”. I still don't feel confident enough to decide when to use each on a table. In theory there is a slight difference in update performance as the engine needs to enforce uniqueness in a unique index, but in reality this is one going to be at most a few CPU cycles per row difference so will be unnoticeable. Jul 17, 2024 · Understanding the differences between an index vs primary key is essential in this context. They are synonyms. By leveraging these tools, databases like TiDB can achieve remarkable performance and reliability. Jul 23, 2025 · Effective indexing is crucial for optimizing query performance in MySQL databases. Sep 23, 2024 · Optimize your MySQL database with our comprehensive guide on MySQL Indexes, covering types, benefits, and effective indexing strategies for better performance. Single-level indexes excel in scenarios with tables containing a few rows or columns with few distinct values. Some say they are synonymous, others give some differences. It has an associated index, for fast query performance. 7. . Learn how to use the MySQL PRIMARY KEY to ensure unique, non-null values in your database tables, enhancing data integrity and optimizing performance with practical examples and best practices. Use index to Jul 23, 2025 · The UNIQUE INDEX is a strong way of doing this. Sep 4, 2015 · I dump database and i have one question. Understanding these types will help you choose the right index for any of your database needs. What's the fastest way to insert into the table, by keeping the domain unique cons To force MySQL to use or ignore an index listed in the possible_keys column, use FORCE INDEX, USE INDEX, or IGNORE INDEX in your query. Only create a unique index for values that you know should be Nov 21, 2023 · Learn how to create primary keys, indices, and composite keys in MySQL to optimize database performance and establish relationships. Apr 16, 2019 · 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. A primary index is automatically created when a primary key is defined on the table. 4, this is no longer allowed deprecated, and the server rejects any CREATE TABLE or ALTER TABLE statement affecting a partitioned table in Jun 21, 2016 · When I want a column to have distinct values, I can either use a constraint create table t1( id int primary key, code varchar(10) unique NULL ); go or I can use a unique index create table t2( id Oct 1, 2025 · The relationship between customer_id keys and individual customer details is straightforward. Jul 23, 2025 · MySQL supports a variety of indexes so that they can perform different functions in the event of different use cases. 1. Columns like status or category, for example, are good candidates. Aug 15, 2025 · Learn how to use PRIMARY KEY indexes in MySQL - a type of B-tree index designed to help a database organize data. To force MySQL to use or ignore an index listed in the possible_keys column, use FORCE INDEX, USE INDEX, or IGNORE INDEX in your query. Indexes are visible by default. If you are using a transactional storage engine such as InnoDB, MySQL automatically rolls back the statement. An index is a performance optimisation feature that enables data to be accessed faster. This article will take it through understanding, implementing, and using the UNIQUE INDEX functionality in MySQL databases. 1, “How MySQL Uses Indexes”. In other words, unlike primary and unique keys, multiple keys permit duplicate values, which makes them suitable for columns where we expect repeated values. There may be some border cases where the size of Systems that rely on this type of single-value lookup are known as “key-value stores”; to use MySQL for such applications, use hash indexes wherever possible. These three are exactly the division of indexes, primary key index, unique index and ordinary index (index). Using SHOW INDEXES FROM customer you can see your unique keys are in fact B-tree type indexes. Secondary indexes, or non-clustered indexes, are separate from the data and maintain pointers to the data rows, allowing for faster access on non-primary key columns. For more information, see Section 15. Mar 26, 2025 · A multiple key is an index in MySQL that allows duplicate values in the column or columns it covers. The primary key for a table represents the column or set of columns that you use in your most vital queries. UNIQUE INDEX UNIQUE INDEX is a database constraint that assures the uniqueness of values in a defined column or collection of columns. 1. This blog will explore different types of indexes in MySQL, ordered by their efficiency: primary key, unique index, composite index, covering index, full-text index, and functional index. A foreign key relationship involves a parent table that holds the initial column values, and a child table with column values that reference the parent column values. 12 Invisible Indexes MySQL supports invisible indexes; that is, indexes that are not used by the optimizer. InnoDB supports secondary indexes on virtual columns. For MyISAM tables, myisamchk --analyze does the same. In this context, VARCHAR and CHAR are considered the same if they are declared as the same size. Jun 21, 2024 · A key is not a kind of index! A key (minimal superkey) is a set of attributes, the values of which are unique for every tuple. 5. Apr 5, 2021 · Differences between INDEX, PRIMARY, UNIQUE, and KEY in MySQL? An index allows duplicate values and NULL values in a column. In a MySQL database I have a table with the following primary key PRIMARY KEY id (invoice, item) In my application I will also frequently be selecting on item by itself and less frequently on only May 5, 2016 · I am using mysql 5. MySQL can use indexes on columns more efficiently if they are declared as the same type and size. Nov 29, 2016 · Dear all, I am trying to dig into the exact difference between key and index in MySQL tables. And unless using SQL Server, an index doesn't ensure uniqueness. Non-Clustered: In MySQL, a primary index is often referred to as a clustered index because it determines the physical order of data in the table. MySQL supports foreign keys, which permit cross-referencing related data across tables, and foreign key constraints, which help keep the related data consistent. Without an index (assuming no other aid, such as a table of contents) you'd have to go through the pages one by one, until you found the topic (that's a "full table scan"). From the CREATE TABLE manual entry: KEY is normally a synonym for INDEX. 16 What is the difference between the following DDL statements? 1) create table sql_query ( id int not null , query_text varchar(21826) not null , query_md5 binar Clustered vs. Oct 3, 2012 · 10. 3. Feb 1, 2025 · MySQL 8 Indexing Best Practices: Learn how to optimize queries, improve database performance, and choose the right indexes with hands-on examples. In mysql, key and index are synonymous. This was implemented for compatibility with other database systems. Typically, the clustered index is synonymous with the primary key. It uses a B-Tree to manage the index. 1 PRIMARY KEY and UNIQUE Index Constraints Normally, errors occur for data-change statements (such as INSERT or UPDATE) that would violate primary-key, unique-key, or foreign-key constraints. Only create a unique index for values that you know should be Jul 23, 2025 · Types of MySQL Indexes MySQL supports a variety of indexes so that they can perform different functions in the event of different use cases. To get the best performance from queries, inserts, and other database operations, it is important to understand how InnoDB uses the clustered index to optimize the common lookup and DML operations. In your case ADD KEY will explicitly define index on that field. They are synonyms, though INDEX should be preferred (as INDEX is ISO SQL compliant, while KEY is a MySQL-specific, non-portable, extension). Jun 17, 2020 · There will be no difference for read operations, once written the entries in the index will be the same. May 30, 2022 · The problems raised in the topic can be solved step by step. By following best practices such as identifying high-volume queries, choosing appropriate index columns avoiding over-indexing and regularly monitoring and optimizing indexes we can significantly enhance the efficiency and responsiveness of the MySQL database. The feature applies to indexes other than primary keys (either explicit or implicit). Then this problem can be simplified to the difference between primary key, unique key and index. The key attribute PRIMARY KEY can also be specified as just KEY when given in a column definition. Use a single-level index for simple queries that locate a specific row based on a single column. For MyISAM tables, running ANALYZE TABLE helps the optimizer choose better indexes. What does this query? ALTER TABLE `ps_cart_rule` ADD KEY `id_customer` (`id_customer`,`active`,`date_to`); ALTER TABLE `ps_cart_rule` ADD KEY `id_customer_ Mar 19, 2012 · A unique key is a special case of index, acting like a regular index with added checking for uniqueness. What's the difference between using INDEX vs KEY in MySQL? There's no difference. Primary Index A primary index is automatically created when a primary key is defined on the table. Query performance benefits from the NOT NULL optimization, because it cannot include any NULL values. An index can be associated with a primary key, but it's not required. There's no difference. Jun 18, 2024 · Indexes play a crucial role in database performance, enabling faster query execution and efficient data retrieval. Primary keys and indexes play a pivotal role in this process, ensuring quick access and unique identification of records. In older versions of MySQL, columns using prefixes were permitted when creating, altering, or upgrading a partitioned table, even though they were not included in the table's partitioning key; in MySQL 8. From the CREATE TABLE Jul 17, 2024 · Understanding the differences between an index vs primary key is essential in this context. 9. For more information about indexes, see Section 10. fhhoz s7b cbeu n0v nrobk 3lu 16gqw0 pmjim6r xyshz dtu