== `sqlite/collation.hpp`
[#collation]

A https://www.sqlite.org/datatype3.html#collation[collation] is a comparison operator between two string-like values,
that allows ordering with a custom algorithm.

.Definition
[source,cpp]
----

// Create a collation
template<typename Func>
void create_collation(connection & conn, cstring_ref name, Func && func);
template<typename Func>
void create_collation(connection & conn, cstring_ref name, Func && func, system::error_code &ec);

// Delete an existing collation.
void delete_collation(connection & conn, cstring_ref name, system::error_code & ec);
void delete_collation(connection & conn, cstring_ref name);
----

 conn:: A connection to the database in which to install the collation.
 name:: The name of the collation.
 func:: The function

The function must be callable with two `string_view` and return an int, indicating the comparison results.

.Example
[source,cpp]
----
// a case insensitive string omparison, e.g. from boost.urls
int ci_compare(string_view s0, string_view s1) noexcept;

extern sqlite::connection conn;

// Register the collation
sqlite::create_collation(conn, "iequal", &ci_compare);

// use the collation to get by name, case insensitively
conn.query("select first_name, last_name from people where first_name = 'Klemens' collate iequal;");

// order by names case insensitively
conn.query("select * from people order by last_name collate iequal asc;");
----

