feat: add col_expr operator== and operator!= overloads for named ID types

Allow col_ref comparisons against index_id, check_id, trigger_id, and
other named ID types that expose a static name() method, avoiding the
need to manually convert to std::string.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Pierre-Luc Gagné

CHANGELOG.md

@@ -8,6 +8,10 @@ Versioning follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Added
+
+- `col_expr` `operator==` and `operator!=` overloads for named ID types (`index_id`, `check_id`, `trigger_id`, etc.) — e.g. `col_ref(statistics::index_name{}) == index_id<"uq_symbol_ticker">{}`
+
 ---
 
 ## [4.2.0] – 2026-03-29

lib/include/ds_mysql/sql_core.hpp

@@ -808,6 +808,23 @@ struct col_expr {
     [[nodiscard]] check_expr operator!=(value_type const& val) const {
         return not_equal<Col>(Col{val});
     }
+
+    template <typename T>
+        requires(!std::is_convertible_v<T, value_type> &&
+                 requires {
+                     { T::name() } -> std::convertible_to<std::string_view>;
+                 })
+    [[nodiscard]] check_expr operator==(T const&) const {
+        return equal<Col>(Col{value_type(T::name())});
+    }
+    template <typename T>
+        requires(!std::is_convertible_v<T, value_type> &&
+                 requires {
+                     { T::name() } -> std::convertible_to<std::string_view>;
+                 })
+    [[nodiscard]] check_expr operator!=(T const&) const {
+        return not_equal<Col>(Col{value_type(T::name())});
+    }
     [[nodiscard]] check_expr operator<(value_type const& val) const {
         return less_than<Col>(Col{val});
     }

tests/unit/test_ddl.cpp

@@ -1671,9 +1671,8 @@ suite<"DDL Features"> ddl_features_suite = [] {
     };
 
     "create_index_on instance-based.unique - generates CREATE UNIQUE INDEX"_test = [] {
-        auto const sql = create_index_on(index_id<"uq_test_table_name">{}, test_table{}, test_table::name{})
-                             .unique()
-                             .build_sql();
+        auto const sql =
+            create_index_on(index_id<"uq_test_table_name">{}, test_table{}, test_table::name{}).unique().build_sql();
         expect(sql == "CREATE UNIQUE INDEX uq_test_table_name ON test_table (name);\n"s) << sql;
     };
 

tests/unit/test_dql.cpp

@@ -756,6 +756,30 @@ suite<"DQL col_ref Operators"> dql_col_ref_suite = [] {
             << sql;
     };
 
+    // -------------------------------------------------------------------
+    // named ID types (index_id, check_id, trigger_id, etc.)
+    // -------------------------------------------------------------------
+
+    "col_ref == index_id — generates equal WHERE SQL with name()"_test = [] {
+        using statistics = mysql_metadata::information_schema::statistics;
+        auto const sql = select(statistics::index_name{})
+                             .from(statistics{})
+                             .where(col_ref(statistics::index_name{}) == index_id<"uq_symbol_ticker">{})
+                             .build_sql();
+        expect(sql == "SELECT index_name FROM information_schema.statistics WHERE index_name = 'uq_symbol_ticker'"s)
+            << sql;
+    };
+
+    "col_ref != index_id — generates not_equal WHERE SQL with name()"_test = [] {
+        using statistics = mysql_metadata::information_schema::statistics;
+        auto const sql = select(statistics::index_name{})
+                             .from(statistics{})
+                             .where(col_ref(statistics::index_name{}) != index_id<"uq_symbol_ticker">{})
+                             .build_sql();
+        expect(sql == "SELECT index_name FROM information_schema.statistics WHERE index_name != 'uq_symbol_ticker'"s)
+            << sql;
+    };
+
     // Without parens, & binds first: a | (b & c).
     // Verify the SQL differs so the test above is meaningful.
     "a | (b & c) — default precedence without parens"_test = [] {