Merge pull request #58390 from bharatnc/ncb/system-database-engines

add table system.database_engines

docs/en/operations/system-tables/database_engines.md

@@ -0,0 +1,26 @@
+---
+slug: /en/operations/system-tables/database_engines
+---
+# database_engines
+
+Contains the list of database engines supported by the server.
+
+This table contains the following columns (the column type is shown in brackets):
+
+- `name` (String) — The name of database engine.
+
+Example:
+
+``` sql
+SELECT *
+FROM system.database_engines
+WHERE name in ('Atomic', 'Lazy', 'Ordinary')
+```
+
+``` text
+┌─name─────┐
+│ Ordinary │
+│ Atomic   │
+│ Lazy     │
+└──────────┘
+```

src/Access/ContextAccess.cpp

@@ -155,6 +155,7 @@ namespace
                 "formats",
                 "privileges",
                 "data_type_families",
+                "database_engines",
                 "table_engines",
                 "table_functions",
                 "aggregate_function_combinators",

src/Client/Suggest.cpp

@@ -77,6 +77,7 @@ static String getLoadSuggestionQuery(Int32 suggestion_limit, bool basic_suggesti
     };
 
     add_column("name", "functions", false, {});
+    add_column("name", "database_engines", false, {});
     add_column("name", "table_engines", false, {});
     add_column("name", "formats", false, {});
     add_column("name", "table_functions", false, {});

src/Databases/DatabaseFactory.h

@@ -52,6 +52,8 @@ public:
 
     void registerDatabase(const std::string & name, CreatorFn creator_fn);
 
+    const DatabaseEngines & getDatabaseEngines() const { return database_engines; }
+
 private:
     DatabaseEngines database_engines;
 };

src/Storages/System/StorageSystemDatabaseEngines.cpp

@@ -0,0 +1,25 @@
+#include <DataTypes/DataTypeString.h>
+#include <DataTypes/DataTypesNumber.h>
+#include <Databases/DatabaseFactory.h>
+#include <Storages/System/StorageSystemDatabaseEngines.h>
+
+namespace DB
+{
+
+NamesAndTypesList StorageSystemDatabaseEngines::getNamesAndTypes()
+{
+    return {
+        {"name", std::make_shared<DataTypeString>()},
+    };
+}
+
+void StorageSystemDatabaseEngines::fillData(MutableColumns & res_columns, ContextPtr, const SelectQueryInfo &) const
+{
+    for (const auto & [engine, _] : DatabaseFactory::instance().getDatabaseEngines())
+    {
+        int i = 0;
+        res_columns[i++]->insert(engine);
+    }
+}
+
+}

src/Storages/System/StorageSystemDatabaseEngines.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <DataTypes/DataTypeString.h>
+#include <Storages/System/IStorageSystemOneBlock.h>
+
+namespace DB
+{
+
+class StorageSystemDatabaseEngines final : public IStorageSystemOneBlock<StorageSystemDatabaseEngines>
+{
+protected:
+    void fillData(MutableColumns & res_columns, ContextPtr context, const SelectQueryInfo & query_info) const override;
+
+    using IStorageSystemOneBlock::IStorageSystemOneBlock;
+
+public:
+    std::string getName() const override { return "SystemDatabaseEngines"; }
+
+    static NamesAndTypesList getNamesAndTypes();
+};
+
+}

src/Storages/System/attachSystemTables.cpp

@@ -45,6 +45,7 @@
 #include <Storages/System/StorageSystemSettings.h>
 #include <Storages/System/StorageSystemSettingsChanges.h>
 #include <Storages/System/StorageSystemMergeTreeSettings.h>
+#include <Storages/System/StorageSystemDatabaseEngines.h>
 #include <Storages/System/StorageSystemTableEngines.h>
 #include <Storages/System/StorageSystemTableFunctions.h>
 #include <Storages/System/StorageSystemTables.h>
@@ -132,6 +133,7 @@ void attachSystemTablesServer(ContextPtr context, IDatabase & system_database, b
     attach<StorageSystemAggregateFunctionCombinators>(context, system_database, "aggregate_function_combinators");
     attach<StorageSystemDataTypeFamilies>(context, system_database, "data_type_families");
     attach<StorageSystemCollations>(context, system_database, "collations");
+    attach<StorageSystemDatabaseEngines>(context, system_database, "database_engines");
     attach<StorageSystemTableEngines>(context, system_database, "table_engines");
     attach<StorageSystemContributors>(context, system_database, "contributors");
     attach<StorageSystemUsers>(context, system_database, "users");

tests/queries/0_stateless/02959_system_database_engines.reference

@@ -0,0 +1,3 @@
+Atomic
+Lazy
+Ordinary

tests/queries/0_stateless/02959_system_database_engines.sql

@@ -0,0 +1 @@
+SELECT * FROM system.database_engines WHERE name IN ('Atomic', 'Lazy', 'Ordinary') ORDER BY name;