CLICKHOUSE-3791: Add system table collations

dbms/src/Columns/Collator.cpp

@@ -87,3 +87,14 @@ const std::string & Collator::getLocale() const
 {
     return locale;
 }
+
+std::vector<std::string> Collator::getAvailableCollations() {
+    std::vector<std::string> result;
+#if USE_ICU
+    size_t available_locales_count = ucol_countAvailable();
+    for (size_t i = 0; i < available_locales_count; ++i) {
+        result.push_back(ucol_getAvailable(i));
+    }
+#endif
+    return result;
+}

dbms/src/Columns/Collator.h

 #pragma once
 
 #include <string>
+#include <vector>
 #include <boost/noncopyable.hpp>
 
 struct UCollator;
@@ -15,6 +16,8 @@ public:
 
     const std::string & getLocale() const;
 
+    static std::vector<std::string> getAvailableCollations();
+
 private:
     std::string locale;
     UCollator * collator;

dbms/src/Storages/System/StorageSystemCollations.cpp

+#include <Columns/Collator.h>
+#include <Storages/System/StorageSystemCollations.h>
+
+namespace DB
+{
+void StorageSystemCollations::fillData(MutableColumns & res_columns) const
+{
+    for (const auto & collation : Collator::getAvailableCollations())
+    {
+        res_columns[0]->insert(collation);
+    }
+}
+}

dbms/src/Storages/System/StorageSystemCollations.h

+#pragma once
+#include <Storages/System/IStorageSystemWithStringColumns.h>
+#include <ext/shared_ptr_helper.h>
+
+namespace DB
+{
+class StorageSystemCollations : public ext::shared_ptr_helper<StorageSystemCollations>,
+                                public IStorageSystemWithStringColumns<StorageSystemCollations>
+{
+protected:
+    void fillData(MutableColumns & res_columns) const override;
+
+public:
+    using IStorageSystemWithStringColumns::IStorageSystemWithStringColumns;
+
+    std::string getName() const override
+    {
+        return "SystemTableCollations";
+    }
+
+    static std::vector<String> getColumnNames()
+    {
+        return {"name"};
+    }
+};
+}

dbms/src/Storages/System/attachSystemTables.cpp

@@ -4,6 +4,7 @@
 #include <Storages/System/StorageSystemAggregateFunctionCombinators.h>
 #include <Storages/System/StorageSystemAsynchronousMetrics.h>
 #include <Storages/System/StorageSystemBuildOptions.h>
+#include <Storages/System/StorageSystemCollations.h>
 #include <Storages/System/StorageSystemClusters.h>
 #include <Storages/System/StorageSystemColumns.h>
 #include <Storages/System/StorageSystemDatabases.h>
@@ -50,6 +51,7 @@ void attachSystemTablesLocal(IDatabase & system_database)
     system_database.attachTable("table_functions", StorageSystemTableFunctions::create("table_functions"));
     system_database.attachTable("aggregate_function_combinators", StorageSystemAggregateFunctionCombinators::create("aggregate_function_combinators"));
     system_database.attachTable("data_type_families", StorageSystemDataTypeFamilies::create("data_type_families"));
+    system_database.attachTable("collations", StorageSystemCollations::create("collations"));
 }
 
 void attachSystemTablesServer(IDatabase & system_database, bool has_zookeeper)