The collation to apply for an ORDER BY clause is simply the collation of the sort key. This happens, for example, with ORDER BY clauses and function or operator calls such as <. When the database system has to perform an ordering or a character classification, it uses the collation of the input expression. In such cases, ordering operations and other operations that need to know the collation will fail. It is also possible for an expression's collation to be indeterminate. The collation of an expression can be the “ default” collation, which means the locale settings defined for the database. The collation of a more complex expression is derived from the collations of its inputs, as described below. If the expression is a constant, the collation is the default collation of the data type of the constant. User-defined base types can also be marked collatable, and of course a domain over a collatable data type is collatable.) If the expression is a column reference, the collation of the expression is the defined collation of the column. (The built-in collatable data types are text, varchar, and char.

Conceptually, every expression of a collatable data type has a collation.

Collate data