Collate

COLLATE refers to a set of rules that govern how textual data is compared and ordered in a database or programming environment. A collation determines the character ordering, case sensitivity, accent sensitivity, and other locale-specific behaviors used during comparisons, sorts, and index lookups. Collations are typically tied to a character set and locale, and they can be chosen to support language-appropriate behavior or fast binary comparisons.

In SQL databases, COLLATE can be applied at multiple levels. It can be specified per column when defining a table, per expression in a query, or at the database or server level. By applying a specific collation, applications can ensure that string operations align with the desired linguistic or cultural expectations. Collations often come in variants such as binary collations, which compare data by raw bytes and are fast but locale-insensitive, and linguistic collations, which implement locale-specific rules for ordering and equality.

Common distinctions among collations include case sensitivity (case-insensitive versus case-sensitive), accent sensitivity (accent-insensitive versus accent-sensitive), and width or kana sensitivity in certain locales. Different database systems provide different naming conventions and options, for example utf8mb4_general_ci in MySQL for a case-insensitive, accent-insensitive Unicode collation, or COLLATE "en_US.utf8" in PostgreSQL to apply a specific locale.

The choice of collation affects query results, index performance, and data integrity. Incorrect collations can lead to unexpected sorting orders or comparisons, such as treating distinct characters as equal or vice versa. Planning collations is an important part of database design, especially for multilingual applications and environments with locale-specific requirements.