🐛 fix(mysql): 补充 PolarDB-X 数据库列表回退查询

Fixes #455

internal/db/mysql_impl.go

@@ -592,6 +592,7 @@ func normalizeMySQLAddress(host string, port int) string {
 var mysqlDatabaseQueries = []string{
 	"SHOW DATABASES",
 	"SELECT DATABASE() AS `Database`",
+	"SELECT schema_name AS database_name FROM information_schema.schemata ORDER BY schema_name",
 }
 
 var mysqlDatabaseNameKeys = []string{

internal/db/mysql_metadata_test.go

@@ -98,6 +98,10 @@ func TestCollectMySQLDatabaseNames_ReturnsOriginalErrorWhenNoDatabaseResolved(t
 			return []map[string]interface{}{
 				{"Database": nil},
 			}, nil, nil
+		case mysqlDatabaseQueries[2]:
+			return []map[string]interface{}{
+				{"database_name": nil},
+			}, nil, nil
 		default:
 			return nil, nil, errors.New("unexpected query")
 		}
@@ -110,6 +114,36 @@ func TestCollectMySQLDatabaseNames_ReturnsOriginalErrorWhenNoDatabaseResolved(t
 	}
 }
 
+func TestCollectMySQLDatabaseNames_FallsBackToInformationSchemaSchemata(t *testing.T) {
+	t.Parallel()
+
+	got, err := collectMySQLDatabaseNames(func(query string) ([]map[string]interface{}, []string, error) {
+		switch query {
+		case mysqlDatabaseQueries[0]:
+			return nil, nil, errors.New("show databases denied")
+		case mysqlDatabaseQueries[1]:
+			return []map[string]interface{}{
+				{"Database": nil},
+			}, nil, nil
+		case mysqlDatabaseQueries[2]:
+			return []map[string]interface{}{
+				{"SCHEMA_NAME": "leite-finance"},
+				{"database_name": "analytics"},
+			}, []string{"SCHEMA_NAME", "database_name"}, nil
+		default:
+			return nil, nil, errors.New("unexpected query")
+		}
+	})
+	if err != nil {
+		t.Fatalf("collectMySQLDatabaseNames 返回错误: %v", err)
+	}
+
+	want := []string{"leite-finance", "analytics"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("unexpected database names, got=%v want=%v", got, want)
+	}
+}
+
 func TestBuildMySQLShowCreateTableQueryNormalizesQuotedIdentifiers(t *testing.T) {
 	t.Parallel()