Join Syntax

Vertica supports the ANSI SQL-92 standard for joining tables, as follows:

table‑reference [join-type] JOIN table-reference [ ON join-predicate ]

where join-type can be one of the following:

For example:

=> SELECT * FROM T1 INNER JOIN T2 ON T1.id = T2.id;

The ON join-predicate clause is invalid for NATURAL and CROSS joins, required for all other join types.

Alternative Syntax Options

Vertica also supports two older join syntax conventions:

Join specified by WHERE clause join predicate

INNER JOIN is equivalent to a query that specifies its join predicate in a WHERE clause. For example, this example and the previous one return equivalent results. They both specify an inner join between tables T1 and T2 on columns T1.id and T2.id, respectively. 

=> SELECT * FROM T1, T2 WHERE T1.id = T2.id;

JOIN USING clause

You can join two tables on identically named columns with a JOIN USING clause. For example:

=> SELECT * FROM T1 JOIN T2 USING(id);

By default, a join that is specified by JOIN USING is always an inner join.

JOIN USING joins the two tables by combining the two join columns into one. Therefore, the two join column data types must be the same or compatible—for example, FLOAT and INTEGER—regardless of the actual data in the joined columns.

Benefits of SQL-92 Join Syntax

Vertica recommends that you use SQL-92 join syntax for several reasons:

  • SQL-92 outer join syntax is portable across databases; the older syntax was not consistent between databases.
  • SQL-92 syntax provides greater control over whether predicates are evaluated during or after outer joins. This was also not consistent between databases when using the older syntax.
  • SQL-92 syntax eliminates ambiguity in the order of evaluating the joins, in cases where more than two tables are joined with outer joins.