Operators on Tables and Rows
Row Extraction
TUPLE FROM r, SQL has row subqueries. These are just like scalar subqueries except that they may specify more than one column. For example, when appearing in a suitable context, the expression
(SELECT * FROM COURSE WHERE CourseId = CID ('C1'))
Yields the row denoted by
CAST (ROW ('C1', 'Database') AS
ROW (CourseId CID, Title VARCHAR (100)))
A row subquery whose table operand is empty yields a row in which every field is NULL.
Field Extraction: For extracting a field from a row, using dot qualification.