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Among the databases called NoSQL, which is generally a correct description of the characteristics of a key-value store?

  1. AIt can process complex SQL including table joins and subqueries faster than a relational database
  2. BBefore any data is written, the names and types of all columns must be strictly defined as a schema
  3. CIt specializes in the simple operation of reading and writing a value by specifying its key and is easy to scale out across multiple servers, but it is not suited to complex queries such as table joins
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Answer: C. It specializes in the simple operation of reading and writing a value by specifying its key and is easy to scale out across multiple servers, but it is not suited to complex queries such as table joins

NoSQL is a collective term for databases other than relational databases, including key-value, document, column-oriented (wide-column) and graph types. A key-value store saves pairs of a key (identifier) and a value and specializes in the simple operation of retrieving a value by specifying its key. Because data can easily be divided by key and distributed across multiple servers, it is used by web services with very heavy traffic, for example to store information about logged-in users (sessions). On the other hand, it is poor at searching by the contents of values and at complex queries such as table joins, so the application has to work around this. Many products also do not require the format of values to be strictly decided in advance (schemaless). Some products also allow eventual consistency, in which updates are not immediately reflected in all the distributed copies.

  • A. Complex queries with joins and subqueries are a strength of relational databases.
  • B. Many products are characterized by not requiring the format of values to be strictly decided in advance (schemaless).
  • C. Correct. Simple reads and writes by key and easy distribution are its characteristics, and complex queries are its weakness.
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