citext

citext is a data type provided by PostgreSQL through the citext extension. It implements a case-insensitive text type intended for fields where comparisons should ignore letter case, such as usernames or email addresses.

The extension introduces the citext data type whose values are stored as text but are compared in a case-insensitive manner. It supports standard text operators and can be used with B-tree indexes and unique constraints to enforce case-insensitive uniqueness. This makes it convenient for enforcing consistent constraints and performing lookups without needing to transform data on every query.

Usage is straightforward: install the extension with CREATE EXTENSION citext in a database, then declare columns as CITEXT. A citext column can be indexed with a conventional B-tree index, and constraints such as PRIMARY KEY and UNIQUE behave in a case-insensitive way. Queries using equality, ordering, or pattern matching with LIKE or ILIKE on citext values follow the type’s case-insensitive semantics, which can simplify logic for user-facing identifiers.

Limitations and considerations include that citext is PostgreSQL-specific and must be enabled per database. While it simplifies case-insensitive comparisons, it may interact with locale or collation settings in ways that differ from plain text and can have different performance characteristics. An alternative approach is to store text in a regular text column and create functional indexes on lower(column) or use other normalization strategies for case-insensitive lookups.