![]() ![]() This returns the following error message:Ĭannot resolve the collation conflict between “SQL_Latin1_General_CP1_CI_AS” and “French_CS_AI” in the equal to operation. Now I’ll execute a query that joins the two tables based on the column name: Notice that in addition to designating CONTAINMENT = NONE, I used a collation that was different from the SQL Server instance default.Īnd next, I’m going to create two tables – one regular table and one temporary in the newly created database, and then insert identical rows: Next I’ll create a database that does NOT allow containment, so you can see the pre-2012 behavior: This returns SQL_Latin1_General_CP1_CI_AS. I’ll start by executing the following in order to determine the default collation of the instance: I see this new behavior as a benefit, but rather than tell you about it, I’ll step through a demonstration instead.įirst of all, this demonstration is on SQL Server (SQL Server 2012 RC0). The SQL Server 2012 contained database feature has an interesting behavior when it comes to collation considerations between the SQL Server instance default collation and a user database collation. SQL syntaxĬollated strings are used as normal strings in SQL, but have a COLLATE clause appended to them.Ĭolumn syntax: STRING COLLATE. In the event that a collation change produces undesired effects, the computed column can be dropped and recreated. To prevent collated data from being invalidated by Unicode changes, we recommend storing data in columns with an uncollated string type, and then using a computed column for the desired collation. As a result, it is possible for a collation change to invalidate existing collated string data. CockroachDB updates its support with new versions of the Unicode standard every year, but there is currently no way to specify the version of Unicode to use. While changes to collations are rare, they are possible, especially in languages with a large numbers of characters (e.g., Simplified and Traditional Chinese). Setting the ks to level2 makes the collation case-insensitive (for languages that have this concept).įor more details on locale extensions, see the Unicode Collation Algorithm. The ks modifier changes the "strength" of the collation, causing it to treat certain classes of characters as equivalent (PostgreSQL calls these "non-deterministic collations"). For example, en-US-u-ks-level2 is case-insensitive US English. To use a locale extension, append -u- to the base locale name, followed by the extension. For example, es-419 (Latin American Spanish) and zh-Hans (Simplified Chinese) are supported, but they do not appear in the pg_collations table because they are equivalent to the es and zh collations listed in the table.ĬockroachDB also supports the following Unicode locale extensions: ![]() ![]() In case of indexed collated strings, collation keys must be stored in addition to the strings from which they are derived, creating a constant factor overhead.ĬockroachDB supports standard aliases for the collations listed in pg_collation. For example, strings containing the character é produce larger collation keys in the French locale than in Chinese.Ĭollated strings that are indexed require additional disk space as compared to uncollated strings. We recommend this because every time a collated string is constructed or loaded into memory, CockroachDB computes its collation key, whose size is linear in relationship to the length of the collated string, which requires additional resources.Ĭollated strings can be considerably larger than the corresponding uncollated strings, depending on the language and the string content. Only use the collation feature when you need to sort strings by a specific collation. However, it is possible to add or overwrite a collation on the fly. Operations on collated strings cannot involve strings with a different collation or strings with no collation. A collation is a set of rules used for ordering and usually corresponds to a language, though some languages have multiple collations with different rules for sorting for example Portuguese has separate collations for Brazilian and European dialects ( pt-BR and pt-PT respectively). For example, in German accented letters are sorted with their unaccented counterparts, while in Swedish they are placed at the end of the alphabet. The COLLATE feature lets you sort STRING values according to language- and country-specific rules, known as collations.Ĭollated strings are important because different languages have different rules for alphabetic order, especially with respect to accented letters. ![]()
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