Why can a candidate key be null?

by


Candidate key is the set of attributes by which it is possible to identify each row of the table. Therefore, if some attribute is nullable, it cannot be one of candidate keys.

Can a candidate key have a null value?

Any attribute of Primary key can not contain NULL value. While in Candidate key any attribute can contain NULL value.

Can any candidate key be a primary key?

Note that each candidate key can be a primary key, but only one should be chosen as the primary key. The rule to become a primary key among candidate keys is that the key’s attribute values must be unique and can never be Null for any domain.

You may also like:

What’s the Deal with com.sec.unifiedwfc and What They Do?
Unified Web Filter is a content filtering service that can be used to block websites or other online content. Unified Web Filter is a content filtering service that can be used to block websites or other online content. Administrators are able to set up rules for different devices within their network, and then apply these…

How subquery is executed?
Each subquery is executed once for every row of the outer query. A correlated subquery is evaluated once for each row processed by the parent statement. The parent statement can be a SELECT, UPDATE, or DELETE statement. Do subqueries execute first? Answer: D. The sub-query always executes before the execution of the main query. Subqueries…

What is type 1 and type 2 error Python?
Type I error occurs when the Null Hypothesis (H0) is mistakenly rejected. This is also referred to as the False Positive Error. Type II errorType II errorA false negative error, or false negative, is a test result which wrongly indicates that a condition does not hold. For example, when a pregnancy test indicates a woman…

Which MySQL engine is faster?
Different storage engines provide better performance in one situation over another. For general use, there are two contenders to be considered. These are MyISAM, which is the default MySQL storage engine, or InnoDB, which is an alternative engine built-in to MySQL intended for high-performance databases. Which MySQL engine is best for performance? Different storage engines…

What is a syntax error in SQL?
Overview. This SQL error generally means that somewhere in the query, there is invalid syntax. Some common examples: Using a database-specific SQL for the wrong database (eg BigQuery supports DATE_ADD, but Redshift supports DATEADD) Typo in the SQL (missing comma, misspelled word, etc) How do I check SQL query syntax? To check syntax code: First,…

What are syntax examples?
Syntax is the order or arrangement of words and phrases to form proper sentences. The most basic syntax follows a subject + verb + direct object formula. That is, “Jillian hit the ball.” Syntax allows us to understand that we wouldn’t write, “Hit Jillian the ball.” What are the types of syntax and give examples?…

What is semantic view in SQL?
Semantic SQL is simple to create SQL queries with no Joins or Union statements. The semantic SQL queries are formulated in standard SQL and query the semantic business model (ontology) mapped to the data, instead of querying the data directly. It is also used to query Views created with the semantic model. What are semantics…

How many types of errors are there?
Generally errors are classified into three types: systematic errors, random errors and blunders. What are the types of errors Class 11? 1) Instrumental error: This error occurs due to poor calibration of the measuring device or the measuring apparatus. 2) Observational error: This error occurs due to poor observation by the observer, while taking measurements.…