Add function getSetting().

src/Functions/getSetting.cpp

@@ -0,0 +1,67 @@
+#include <Functions/IFunctionImpl.h>
+#include <Functions/FunctionFactory.h>
+#include <Functions/FunctionHelpers.h>
+#include <DataTypes/FieldToDataType.h>
+#include <Interpreters/convertFieldToType.h>
+#include <Interpreters/Context.h>
+#include <Core/Field.h>
+
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
+    extern const int ILLEGAL_COLUMN;
+}
+
+/// Get the value of a setting.
+class FunctionGetSetting : public IFunction
+{
+public:
+    static constexpr auto name = "getSetting";
+
+    static FunctionPtr create(const Context & context_) { return std::make_shared<FunctionGetSetting>(context_); }
+    explicit FunctionGetSetting(const Context & context_) : context(context_) {}
+
+    String getName() const override { return name; }
+    bool isDeterministic() const override { return false; }
+    size_t getNumberOfArguments() const override { return 1; }
+    ColumnNumbers getArgumentsThatAreAlwaysConstant() const override { return {0}; }
+
+    DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
+    {
+        if (!isString(arguments[0].type))
+            throw Exception{"The argument of function " + String{name} + " should be a constant string with the name of a setting",
+                            ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT};
+        const auto * column = arguments[0].column.get();
+        if (!column || !checkAndGetColumnConstStringOrFixedString(column))
+            throw Exception{"The argument of function " + String{name} + " should be a constant string with the name of a setting",
+                            ErrorCodes::ILLEGAL_COLUMN};
+
+        std::string_view setting_name{column->getDataAt(0)};
+        value = context.getSettingsRef().get(setting_name);
+
+        DataTypePtr type = applyVisitor(FieldToDataType{}, value);
+        value = convertFieldToType(value, *type);
+        return type;
+    }
+
+    void executeImpl(Block & block, const ColumnNumbers &, size_t result, size_t input_rows_count) const override
+    {
+        block.getByPosition(result).column = block.getByPosition(result).type->createColumnConst(input_rows_count, value);
+    }
+
+private:
+    mutable Field value;
+    const Context & context;
+};
+
+
+void registerFunctionGetSetting(FunctionFactory & factory)
+{
+    factory.registerFunction<FunctionGetSetting>();
+}
+
+}

src/Functions/registerFunctionsMiscellaneous.cpp

@@ -56,6 +56,7 @@ void registerFunctionBasename(FunctionFactory &);
 void registerFunctionTransform(FunctionFactory &);
 void registerFunctionGetMacro(FunctionFactory &);
 void registerFunctionGetScalar(FunctionFactory &);
+void registerFunctionGetSetting(FunctionFactory &);
 void registerFunctionIsConstant(FunctionFactory &);
 void registerFunctionGlobalVariable(FunctionFactory &);
 void registerFunctionHasThreadFuzzer(FunctionFactory &);
@@ -116,6 +117,7 @@ void registerFunctionsMiscellaneous(FunctionFactory & factory)
     registerFunctionTransform(factory);
     registerFunctionGetMacro(factory);
     registerFunctionGetScalar(factory);
+    registerFunctionGetSetting(factory);
     registerFunctionIsConstant(factory);
     registerFunctionGlobalVariable(factory);
     registerFunctionHasThreadFuzzer(factory);

src/Functions/ya.make

@@ -202,6 +202,7 @@ SRCS(
     geoToH3.cpp
     getMacro.cpp
     getScalar.cpp
+    getSetting.cpp
     getSizeOfEnumType.cpp
     globalVariable.cpp
     greatCircleDistance.cpp