Bissoy.com
Doctors Medicines MCQs Q&A

What is true about Unique and primary key?

What is true about Unique and primary key? Correct Answer Unique can have single NULL value but Primary can’t have even single.

Primary key doesn’t allow Null values and Unique key allows Null value, but only one Null value.

Related Questions

Public key encryption uses multiple keys.ne key is used to encrypt data, while another is used to decrypt data.he key used to encrypt data is called the _______ key, while the key used to decrypt data is called the ________ key.
Given 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?
Two statements are given followed by two conclusions I and II. You have to consider these statements to be true, even if they seem to be at variance with commonly known facts and choose which f the given conclusions logically follow(s) from the given statements. Statements : All Chairs are expensive All expensive are unique. Conclusion : I. All chairs are unique. II. All unique are expensive.
Let G be any connected, weighted, undirected graph. I. G has a unique minimum spanning tree, if no two edges of G have the same weight. II. G has a unique minimum spanning tree, if, for every cut of G, there is a unique minimum-weight edge crossing the cut. Which of the above two statements is/are TRUE?
From an alloy, two specimens are machined and tested separately under tension and compression. The engineering stress-strain curves as well as the true stress-true strain curves for tension and compression are plotted in the same diagram. Identify the correct statements:
P. The engineering stress-strain curves in tension and compression are identical.
Q. The true stress-true strain curve in compression is lower than the true stresstrue strain curve in tension due to Bauschinger effect.
R. The true stress-true strain curve in tension is above the corresponding engineering stress-strain, curve.
S. The true stress-true strain curve in tension and compression are identical.
An enterprise key is a primary key whose value is unique for a given relation.
Error code for The statement was aborted because it would have caused a duplicate key value in a unique or primary key constraint.
A pulley is connected to a power transmission shaft of diameter d by means of a rectangular sunk key of width w and length l. The width of the key is taken as d/4. For full power transmission, the shearing strength of the key is equal to the torsional shearing strength of the shaft. The ratio of the length of the key to the diameter of the shaft (l/d) is
A private key and its mathematically related public key, which are so related that the public key, can verify a digital signature created by the private key, in an Asymmetric Crypto system means:
The primary key of the representation of a weak entity set consists of the primary key of the strong entity set and the _______