How to CREATE INDEX in MySQL

Galaxy Glossary

How do I create and use indexes in MySQL to accelerate queries?

CREATE INDEX adds a secondary lookup structure to a MySQL table, dramatically reducing search time on the indexed columns.

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Description

Why should I use CREATE INDEX?

CREATE INDEX speeds up SELECT, JOIN, and ORDER BY operations by letting MySQL jump directly to matching rows instead of scanning the entire table.

What is the basic syntax?

Use CREATE INDEX index_name ON table_name (column1[, column2 ...]); Include column order for composite indexes to match your most common WHERE clauses.

How do I name indexes clearly?

Follow the pattern tbl_column_idx (e.g., orders_customer_id_idx). Clear names simplify maintenance and troubleshooting.

Which columns should I index?

Target columns frequently used in WHERE, JOIN, or ORDER BY clauses, such as Orders.customer_id or OrderItems.order_id.

Can I create unique indexes?

Yes. UNIQUE indexes enforce column uniqueness and improve lookups. Use UNIQUE INDEX for columns like Customers.email.

How do I monitor index size?

Query INFORMATION_SCHEMA.STATISTICS and TABLES to track index_cardinality and data_length. Drop unused or redundant indexes to save space.

Best practices for ecommerce databases?

Index foreign keys (customer_id, product_id), high-selectivity columns (email), and composite combinations that mirror frequent multi-column filters.

Why How to CREATE INDEX in MySQL is important

How to CREATE INDEX in MySQL Example Usage


-- Find total spent by a specific customer faster
CREATE INDEX orders_customer_id_idx ON Orders (customer_id);

SELECT c.name,
       SUM(o.total_amount) AS lifetime_value
FROM Customers c
JOIN Orders   o ON o.customer_id = c.id
WHERE c.id = 42
GROUP BY c.name;

How to CREATE INDEX in MySQL Syntax


CREATE [UNIQUE|FULLTEXT|SPATIAL] INDEX index_name
    [USING {BTREE|HASH}]
    ON table_name (col1 [ASC|DESC] [, col2 ...])
    [VISIBLE | INVISIBLE]

-- Example: speed up customer lookups in Orders
CREATE INDEX orders_customer_id_idx
    ON Orders (customer_id);

-- Composite example: optimize product sales queries
CREATE INDEX orderitems_product_qty_idx
    ON OrderItems (product_id, quantity DESC);

Common Mistakes

Indexing low-cardinality columns such as status or gender. These values repeat often, so MySQL still scans many rows. Instead, index columns with high selectivity like email or id.
Creating overlapping indexes (e.g., (customer_id) and (customer_id, order_date)). The longer composite covers the shorter, so drop redundant ones to save space and write speed.

Frequently Asked Questions (FAQs)

Does adding an index slow INSERTs?

Yes. Each INSERT, UPDATE, or DELETE must update the index tree. The read speed gain usually outweighs the write overhead for analytics workloads.

How many indexes are too many?

There is no hard limit, but every extra index consumes storage and write time. Audit indexes periodically; keep only those referenced by queries.

Can I make an index invisible?

MySQL 8 lets you mark an index INVISIBLE to test performance impact without dropping it. Queries will ignore it until you set it VISIBLE again.

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