Project ForgeGiven the following statements:
S1: A foreign key declaration can always be replaced by an equivalent check assertion in SQL. S2: Given the table R(a,b,c) where a and b together form the primary key, the following is a valid table definition: CREATE TABLE S ( a INTEGER, d INTEGER, e INTEGER, PRIMARY KEY (d), FOREIGN KEY (a) references R)
Which one of the following statements is CORRECT?
- AS1 is TRUE and S2 is FALSE.
- BBoth S1 and S2 are TRUE.
- CS1 is FALSE and S2 is TRUE.
- Both S1 and S2 are FALSE.
Explanation
S1 is FALSE: in standard SQL, CHECK constraints cannot reliably enforce cross-table referential integrity the way a FOREIGN KEY declaration does (there is no guaranteed subquery-based equivalent that behaves identically under all inserts/updates/deletes to the referenced table). S2 is FALSE: R's primary key is the 2-column combination (a,b), so a FOREIGN KEY declaration on just the single column (a) cannot validly reference R — a foreign key must match the full arity of the referenced table's primary key (or another candidate key). So both S1 and S2 are FALSE.
Source: GATE CS 2014 (Session 1) (2014)
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