Add numeric default aliases and document tagged usage

Author: Pierre-Luc Gagné

README.md

@@ -48,6 +48,11 @@ struct product {
 //   using price = tagged_column_field<price_tag, double>;
 //   price price_;
 //   // IMPORTANT: tag structs must be nested inside the table struct — not at global scope.
+//
+//   // For wrapper types with default template parameters, use the provided aliases:
+//   struct amount_tag {};
+//   using amount = tagged_column_field<amount_tag, decimal_type_default>;
+//   amount amount_;
 
 // c) Fixed string literal — column name embedded directly, no tag needed.
 //    ⚠ Two tables with identically-named and -typed columns share the same C++ type,
@@ -259,16 +264,27 @@ auto r2 = db.validate_database<my_db>();
 ```cpp
 struct event {
     COLUMN_FIELD(id,         uint32_t)
-    COLUMN_FIELD(created_at, datetime_type)           // DATETIME — defaults to NOW()
-    COLUMN_FIELD(updated_at, timestamp_type)          // TIMESTAMP — defaults to NOW()
-    COLUMN_FIELD(duration,   time_type)               // TIME
-    COLUMN_FIELD(started_at, std::optional<datetime_type>)  // nullable DATETIME
+    COLUMN_FIELD(created_at, datetime_type<>)           // DATETIME — defaults to NOW()
+    COLUMN_FIELD(updated_at, timestamp_type<>)          // TIMESTAMP — defaults to NOW()
+    COLUMN_FIELD(duration,   time_type<>)               // TIME
+    COLUMN_FIELD(started_at, std::optional<datetime_type<>>)  // nullable DATETIME
 };
 
 // Fractional-second precision (0–6) is set on the value object:
 event row;
-row.created_at_  = datetime_type{tp, 3};   // DATETIME(3)
-row.duration_    = time_type{std::chrono::milliseconds{1500}, 3};  // TIME(3) = 00:00:01.500
+row.created_at_  = datetime_type<>{tp, 3};   // DATETIME(3)
+row.duration_    = time_type<>{std::chrono::milliseconds{1500}, 3};  // TIME(3) = 00:00:01.500
+
+// Non-macro form with concise aliases:
+struct audit_event {
+    struct created_at_tag {};
+    using created_at = tagged_column_field<created_at_tag, datetime_type_default>;
+    created_at created_at_;
+
+    struct amount_tag {};
+    using amount = tagged_column_field<amount_tag, decimal_type_default>;
+    amount amount_;
+};
 ```
 
 ### Numeric Precision Overrides

lib/include/ds_mysql/numeric_field.hpp

@@ -110,6 +110,10 @@ struct decimal_type : detail::formatted_numeric_base<decimal_type<Precision, Sca
     }
 };
 
+using float_type_default = float_type<>;
+using double_type_default = double_type<>;
+using decimal_type_default = decimal_type<>;
+
 template <typename T>
 struct is_formatted_numeric_type : std::false_type {};
 

tests/unit/test_ddl.cpp

@@ -111,6 +111,24 @@ struct tagged_temporal_alias_table {
     duration duration_;
 };
 
+struct tagged_numeric_alias_table {
+    struct id_tag {};
+    using id = tagged_column_field<id_tag, uint32_t>;
+    id id_;
+
+    struct value0_tag {};
+    using value0 = tagged_column_field<value0_tag, float_type_default>;
+    value0 value0_;
+
+    struct value1_tag {};
+    using value1 = tagged_column_field<value1_tag, double_type_default>;
+    value1 value1_;
+
+    struct value2_tag {};
+    using value2 = tagged_column_field<value2_tag, decimal_type_default>;
+    value2 value2_;
+};
+
 struct symbol_with_indexes {
     COLUMN_FIELD(id, int32_t)
     COLUMN_FIELD(exchange_id, std::optional<int32_t>)
@@ -303,6 +321,22 @@ suite<"DDL"> ddl_suite = [] {
             << sql;
     };
 
+    "tagged_column_field with numeric default aliases - emits FLOAT/DOUBLE/DECIMAL"_test = [] {
+        expect(sql_type_for<float_type_default>() == "FLOAT"s);
+        expect(sql_type_for<double_type_default>() == "DOUBLE"s);
+        expect(sql_type_for<decimal_type_default>() == "DECIMAL"s);
+
+        auto const sql = create_table<tagged_numeric_alias_table>().build_sql();
+        expect(sql ==
+               "CREATE TABLE tagged_numeric_alias_table (\n"
+               "    id INT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,\n"
+               "    value0 FLOAT NOT NULL,\n"
+               "    value1 DOUBLE NOT NULL,\n"
+               "    value2 DECIMAL NOT NULL\n"
+               ");\n"s)
+            << sql;
+    };
+
     "create_table with numeric sql formatting options - emits FLOAT/DOUBLE/DECIMAL definitions"_test = [] {
         auto const sql = create_table<numeric_format_table>().build_sql();
         expect(sql ==