Fix optimize_uniq_to_count removing the column alias

src/Interpreters/RewriteUniqToCountVisitor.cpp

@@ -156,7 +156,11 @@ void RewriteUniqToCountMatcher::visit(ASTPtr & ast, Data & /*data*/)
     };
 
     if (match_subquery_with_distinct() || match_subquery_with_group_by())
+    {
+        auto main_alias = expr_list->children[0]->tryGetAlias();
         expr_list->children[0] = makeASTFunction("count");
+        expr_list->children[0]->setAlias(main_alias);
+    }
 }
 
 }

tests/queries/0_stateless/02990_optimize_uniq_to_count_alias.reference

@@ -0,0 +1,2 @@
+1
+1

tests/queries/0_stateless/02990_optimize_uniq_to_count_alias.sql

@@ -0,0 +1,37 @@
+--https://github.com/ClickHouse/ClickHouse/issues/59999
+DROP TABLE IF EXISTS tags;
+CREATE TABLE tags (dev_tag String) ENGINE = Memory AS SELECT '1';
+
+SELECT *
+FROM
+(
+    SELECT countDistinct(dev_tag) AS total_devtags
+    FROM
+    (
+        SELECT dev_tag
+        FROM
+            (
+                SELECT *
+                FROM tags
+            ) AS t
+    GROUP BY dev_tag
+    ) AS t
+) SETTINGS optimize_uniq_to_count=0;
+
+SELECT *
+FROM
+(
+    SELECT countDistinct(dev_tag) AS total_devtags
+    FROM
+    (
+        SELECT dev_tag
+        FROM
+            (
+                SELECT *
+                FROM tags
+            ) AS t
+    GROUP BY dev_tag
+    ) AS t
+) SETTINGS optimize_uniq_to_count=1;
+
+DROP TABLE IF EXISTS tags;