![]() Although initial support for ICU collations was added in PostgreSQL 10, using an ICU collation as the default for a cluster or database wasn’t available until PostgreSQL 15. Historically, PostgreSQL users used the collations provided by glibc because those are the defaults on many UNIX systems. As of this writing, the only two collation providers used with PostgreSQL are glibc and the Internal Components of Unicode (ICU) collations. PostgreSQL doesn’t provide its own default collation it uses collation providers. These changes can have consequences that impact the storage of data, particularly around indexes where values may no longer be stored in the expected order. ![]() Notice how the Turkish collation orders the öb string last in its list:Ĭollations can change over time due to the addition of new characters to languages or modifications to ordering rules. ![]() The following example uses PostgreSQL with a German collation (“ de_DE“) and a Turkish collation (“ tr_TR“) to demonstrate how these two collations treat the o and ö characters differently. In relational databases, collations are used when comparing two strings, such as in a JOIN clause, when there is a text column in an ORDER BY clause, and when building and maintaining indexes over text data. In Linux, support for collations most commonly comes from glibc, also known as the standard C library. Collations are a fundamental part of computer systems and are included as part of the operating system. For example, in German, the o character is equivalent to ö for ordering, but in Turkish, o and ö are ordered differently. Collation rules can vary depending on the locale. Collations work alongside character encodings, such as UTF-8, to define how each character should be ordered. Ordering numbers have rules determined by mathematical properties, but how does a database decide how to order text? For example, how does a database decide which of these text characters comes first: A, a, or ä? This is where databases rely on collations.Ī collation is a set of rules that defines how text is ordered. For example, an application may need to sort schedule data from the earliest date to the latest or order by a list of names. We also review how Amazon Relational Database Service (Amazon RDS) and Amazon Aurora can help you manage collations using an independent default collation library, and future work in PostgreSQL on collation handling.Ī fundamental feature in a database is the ability to sort data.
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