How to CREATE INDEX in PostgreSQL

How do I use CREATE INDEX in PostgreSQL to speed up queries?

CREATE INDEX builds a separate lookup structure that accelerates SELECT, JOIN, and ORDER BY operations on one or more table columns.

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Description

What does CREATE INDEX do?

CREATE INDEX builds an auxiliary data structure that lets PostgreSQL locate rows quickly without scanning the whole table. Queries with WHERE, JOIN, ORDER BY, or DISTINCT clauses that match the indexed columns run dramatically faster.

When should I create an index?

Create an index when a column appears frequently in search predicates, joins, or sort operations and its cardinality is high enough that most queries touch a small data subset.

What is the basic syntax of CREATE INDEX?

Use CREATE INDEX index_name ON table (column_expr …). Add modifiers like UNIQUE, CONCURRENTLY, USING, INCLUDE, and WHERE to fine-tune behavior.

How to create a simple B-tree index?

To speed up customer lookups by email: CREATE INDEX idx_customers_email ON Customers (email); PostgreSQL chooses B-tree by default, perfect for equality and range checks.

How to create a unique index to stop duplicates?

Ensure each product name is unique: CREATE UNIQUE INDEX idx_products_name_unique ON Products (name); The index doubles as an enforcement mechanism, rejecting duplicate inserts.

How to speed up indexing with CONCURRENTLY?

Build large indexes without blocking writes: CREATE INDEX CONCURRENTLY idx_orders_date ON Orders (order_date); This keeps the table 100% available but takes longer and can’t run inside a transaction block.

How to index expressions and partial data?

Accelerate case-insensitive searches: CREATE INDEX idx_customers_email_lower ON Customers (lower(email)); Limit index size by storing only active orders: CREATE INDEX idx_orders_active ON Orders (customer_id) WHERE total_amount > 0;

Best practices for CREATE INDEX

Index only what you query. Combine up to three columns for composite indexes, ordering them by selectivity. Drop unused indexes to save RAM and write overhead.

Common mistakes and how to avoid them

Over-indexing: Too many indexes slow writes. Audit with pg_stat_user_indexes and drop duplicates. Wrong column order: In a composite index, place the most selective column first to maximize pruning.

FAQs

Does CREATE INDEX lock the table?

Standard CREATE INDEX blocks writes but not reads. Use CONCURRENTLY to avoid write locks at the cost of a slower build.

Which index method should I choose?

B-tree is default for equality/range. Use GIN for arrays/JSONB, GiST for geometry, and BRIN for huge, naturally ordered tables.

How can I see if an index is used?

Run EXPLAIN on your query or check usage stats in pg_stat_user_indexes.If scans = 0, the index is probably redundant.

Why How to CREATE INDEX in PostgreSQL is important

How to CREATE INDEX in PostgreSQL Example Usage


-- Speed up daily sales dashboards by indexing order date
CREATE INDEX CONCURRENTLY idx_orders_order_date ON Orders (order_date DESC);

-- Prevent duplicate emails during user sign-up
CREATE UNIQUE INDEX idx_customers_email_unique ON Customers (email);

-- Accelerate JSONB product attribute search
CREATE INDEX idx_products_attrs_gin ON Products USING gin (attrs jsonb_path_ops);

How to CREATE INDEX in PostgreSQL Syntax


CREATE [UNIQUE] INDEX [CONCURRENTLY] index_name
    ON table_name [USING {btree | hash | gist | gin | brin}]
    ( column_expression [ASC|DESC] [NULLS {FIRST|LAST}], ... )
    [INCLUDE (column_list)]
    [WITH (storage_parameter = value [, ...])]
    [TABLESPACE tablespace_name]
    [WHERE predicate];
-- Example
CREATE INDEX idx_orderitems_order_product ON OrderItems (order_id, product_id);
CREATE UNIQUE INDEX CONCURRENTLY idx_customers_email_unique ON Customers USING btree (email);

Common Mistakes

Creating indexes on low-cardinality columns like boolean flags. They rarely filter enough rows to justify storage. Instead, create partial indexes or skip indexing.
Running CREATE INDEX inside a transaction block with CONCURRENTLY. PostgreSQL throws an error. Execute the statement outside BEGIN/COMMIT.