Add function: chdb() to return version (#25)

* add function: chdb() to return version

This is an example of a C++ function that returns the current version of chDB as a string. The version number is defined using the CHDB_VERSION_STRING macro, which should be defined during the build process.

The FunctionChdbVersion class is a subclass of FunctionConstantBase, which is a base class for functions that return a constant value. The FunctionChdbVersion constructor takes the CHDB_VERSION_STRING macro as an argument, which is passed to the FunctionConstantBase constructor to set the constant value of the function.

The REGISTER_FUNCTION macro is used to register the FunctionChdbVersion function with the FunctionFactory. The REGISTER_FUNCTION macro should be conditionally compiled using an #if directive that checks whether the CHDB_VERSION_STRING macro is defined, to avoid registering the function if the version number is not available.

* Update chdbVersion.cpp

* Update chdbVersion.cpp

* Update CMakeLists.txt

* Update CMakeLists.txt

src/Functions/CMakeLists.txt

@@ -121,3 +121,7 @@ else()
     add_library(clickhouse_functions SHARED ${OBJECT_LIBS})
     target_link_libraries(clickhouse_functions PUBLIC ${PUBLIC_LIBS} PRIVATE ${PRIVATE_LIBS})
 endif ()
+
+if (CHDB_VERSION)
+    add_compile_definitions(CHDB_VERSION_STRING="${CHDB_VERSION}")
+endif ()

src/Functions/chdbVersion.cpp

@@ -0,0 +1,34 @@
+#if defined(CHDB_VERSION_STRING)
+
+#include <DataTypes/DataTypeString.h>
+#include <Functions/FunctionFactory.h>
+#include <Functions/FunctionConstantBase.h>
+
+namespace DB
+{
+
+namespace
+{
+    /// chdb() - returns the current chdb version as a string.
+    class FunctionChdbVersion : public FunctionConstantBase<FunctionChdbVersion, String, DataTypeString>
+    {
+    public:
+        static constexpr auto name = "chdb";
+        static FunctionPtr create(ContextPtr context) { return std::make_shared<FunctionChdbVersion>(context); }
+        explicit FunctionChdbVersion(ContextPtr context) : FunctionConstantBase(CHDB_VERSION_STRING, context->isDistributed()) {}
+    };
+}
+
+REGISTER_FUNCTION(ChdbVersion)
+{
+    factory.registerFunction<FunctionChdbVersion>(
+        {
+        R"(
+Returns the version of chDB.  The result type is String.
+        )",
+        Documentation::Examples{{"chdb", "SELECT chdb()"}},
+        Documentation::Categories{"String"}
+        }, FunctionFactory::CaseInsensitive);
+}
+}
+#endif