Joe Celko's SQL for Smarties, 3rd Edition

9.2. Row Comparisons in SQL

Standard SQL generalized the theta operators so they would work on row expressions and not just on scalars. This feature is not yet popular, but it is very handy for situations where a key is made from more than one column, and so forth. This makes SQL more orthogonal, and it has an intuitive feel to it. Take three row constants:

A = (10, 20, 30, 40);

B = (10, NULL, 30, 40);

C = (10, NULL, 30, 100);

It seems reasonable to define a row comparison as valid only when the data types of each corresponding column in the rows are union-compatible. If not, the operation is an error and should report a warning. It also seems reasonable to define the results of the comparison to the ANDed results of each corresponding column ...