fix: search by lowercase function name

src/query/sql/src/planner/semantic/type_check.rs

@@ -721,8 +721,9 @@ impl<'a> TypeChecker<'a> {
             } => {
                 let func_name = normalize_identifier(name, self.name_resolution_ctx).to_string();
                 let func_name = func_name.as_str();
-                if !is_builtin_function(func_name)
-                    && !Self::all_sugar_functions().contains(&func_name)
+                let func_name_lowercase = func_name.to_lowercase();
+                if !is_builtin_function(&func_name_lowercase)
+                    && !Self::all_sugar_functions().contains(&func_name_lowercase.as_str())
                 {
                     if let Some(udf) = self.resolve_udf(*span, func_name, args)? {
                         return Ok(udf);

src/query/sql/tests/type_checker.rs

@@ -0,0 +1,54 @@
+// Copyright 2022 Datafuse Labs.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use databend_common_ast::parser::parse_expr;
+use databend_common_ast::parser::tokenize_sql;
+use databend_common_ast::parser::Dialect;
+use databend_common_ast::ast::Expr;
+use databend_common_catalog::table_context::TableContext;
+use databend_common_sql::BindContext;
+use databend_common_sql::MetadataRef;
+use databend_query::sql::NameResolutionContext;
+use databend_common_sql::TypeChecker;
+
+#[test]
+fn test_resolve_function_call_name() {
+    let mut bind_context = BindContext::default();
+    let table_context = Arc::new(TableContext::new());
+    let name_resolution_ctx = NameResolutionContext {
+        unquoted_ident_case_sensitive: true,
+        quoted_ident_case_sensitive: true,
+        deny_column_reference: false,
+    };
+    let metadata = MetadataRef::default();
+    let aliases = vec![];
+
+    let type_checker = TypeChecker::try_create(
+        &mut bind_context,
+        table_context,
+        &name_resolution_ctx,
+        metadata,
+        &aliases,
+        false,
+    );
+
+    let tokens = tokenize_sql("SELECT VERSION();").unwrap();
+    let mut expr = parse_expr(&tokens, Dialect::Mysql).unwrap();
+
+    if let Ok(mut checker) = type_checker {
+        let result = checker.resolve(&expr);
+
+        assert!(result.is_ok(), "Function resolution failed");
+    }
+}