Rowsets

An implementation of RowsetInterface defines a set of database rows that contain columns of data. The Rowset class is an instantiable implementation of RowsetInterface. An instance of Rowsets class is a collection of RowsetInterface objects.

Rowsets is used in Select::from() to define the sets of table(s) from which data is to be retrieved.

Joins

A JOIN clause combines columns from one or more tables into a new table.^[1]

The natural LEFT JOIN of two tables is defined to be semantically equivalent to an INNER JOIN or a LEFT JOIN with a USING clause that names all columns that exist in both tables. ^[2]

RIGHT JOIN works analogously to LEFT JOIN. To keep code portable across databases, it is recommended that you use LEFT JOIN instead of RIGHT JOIN.

Some essential Join methods:

• Join::using() - If columns in an equi-join have the same name, SQL-92 provides an optional shorthand notation for expressing equi-joins. The USING clause is not supported by MS SQL Server and Sybase.^[3]
• Join::on() - indicates the table(s)