add mssql checker (#13)

Co-authored-by: APAHE <[email protected]>

checkers/mssql.go

@@ -0,0 +1,35 @@
+/*
+   Copyright 2020 YANDEX LLC
+
+   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.
+*/
+
+package checkers
+
+import (
+	"context"
+	"database/sql"
+)
+
+// MSSQL checks whether MSSQL server is primary or not.
+func MSSQL(ctx context.Context, db *sql.DB) (bool, error) {
+	var status bool
+
+	if err := db.QueryRowContext(ctx, "SELECT IIF(count(database_guid) = 0, 'TRUE', 'FALSE') AS STATUS "+
+		"FROM sys.database_recovery_status"+
+		" WHERE database_guid IS NULL",
+	).Scan(&status); err != nil {
+		return false, err
+	}
+	return status, nil
+}