default Optional<String> getUpsertStatement(
            String schema, String tableName, String[] fieldNames, String[] uniqueKeyFields, boolean allReplace) {
        return Optional.empty();
    }
Get dialect upsert statement, the database has its own upsert syntax, such as Mysql
using DUPLICATE KEY UPDATE, and PostgresSQL using ON CONFLICT... DO UPDATE SET..

if allReplace is true, new data will replace  previous values such as mysql replace into ..

@return None if dialect does not support upsert statement, the writer will degrade to
the use of select + update/insert, this performance is poor.
rdb/rdb-sink/src/main/java/com/dtstack/flink/sql/sink/rdb/dialect/JDBCDialect.java