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2.2.4 Field Selection

If an expression yields a value of a composite type (row type), then a specific field of the row can be extracted by writing

expression.fieldname

In general the row expression must be parenthesized, but the parentheses can be omitted when the expression to be selected from is just a table reference or positional parameter. For example:

mytable.mycolumn
$1.somecolumn
(rowfunction(a,b)).col3

(Thus, a qualified column reference is actually just a special case of the field selection syntax.) An important special case is extracting a field from a table column that is of a composite type:

(compositecol).somefield
(mytable.compositecol).somefield

The parentheses are required here to show that compositecol is a column name not a table name, or that mytable is a table name not a schema name in the second case.