Right, when we do cross products, we are doing an expansion with respect to the first row.
算外积时，依第一行展开。
2
Percolator was designed to provide cross-row, cross-table ACID-compliant transactions via " snapshot isolation" since many threads on many machines need to transform the repository.
In a cross join, each row from one table is combined with each row from another table, resulting in what is called a cross product or a Cartesian product.