protected void serializeForInsert(QueryMetadata metadata, RelationalPath<?> entity, List<SQLInsertBatch> batches) {
        serializeForInsert(metadata, entity, batches.get(0).getColumns(), batches.get(0).getValues(), null);
        for (int i = 1; i < batches.size(); i++) {
            append(COMMA);
            append("(");
            handle(COMMA, batches.get(i).getValues());
            append(")");
        }
    }
Return a list of expressions that can be used to uniquely define the query sources

@param joins
@return identifier columns
querydsl-sql/src/main/java/com/querydsl/sql/SQLSerializer.java