GATE CS 2014 Set 1 — Question 32
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Databases → SQL → DDL Commands
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Question
Given the following statements:S1: A foreign key declaration can always be replaced by an equivalent check assertion in SQL.S2: Given the table where and together form the primary key, the following is a valid table definition.Which one of the following statements is CORRECT?
CREATE TABLE S (
a INTEGER,
d INTEGER,
e INTEGER,
PRIMARY KEY (d),
FOREIGN KEY (a) references R)
Correct answer
(D) Both S1 and S2 are FALSE.
Solution
S1 is FALSE. While
CHECK constraints can enforce domain integrity and some business rules, they cannot fully replace FOREIGN KEY constraints. Foreign keys enforce referential integrity (ensuring a value exists in another table) and support cascading actions (ON DELETE CASCADE, ON UPDATE CASCADE), which CHECK assertions cannot easily replicate without complex triggers or non-standard SQL features.S2 is FALSE. In standard SQL, a FOREIGN KEY must reference a unique key (Primary Key or Unique Constraint) in the parent table. In table , the primary key is the composite key . The attribute alone is not guaranteed to be unique. Therefore, FOREIGN KEY (a) references R is invalid because it does not reference a candidate key of .Continue learning with Success Tracker
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