GCSE Computer Science:
Structured Query Language (SQL)
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Frequently Asked Questions
What is SQL, and what is its primary purpose?
SQL (Structured Query Language) is a programming language specifically designed for managing and interacting with relational databases. Its primary purpose is to allow users to create, manipulate, and query data within a database using a series of standardized commands.
What are some common SQL commands?
Some common SQL commands include:
- SELECT: Retrieves data from one or more tables in a database.
- INSERT: Adds new rows (records) to a table.
- UPDATE: Modifies existing rows in a table.
- DELETE: Removes rows from a table.
- CREATE TABLE: Creates a new table with specified columns and data types.
- ALTER TABLE: Modifies an existing table's structure (e.g., adding, renaming, or deleting columns).
- DROP TABLE: Deletes an entire table and all its data.
What is a relational database?
A relational database is a type of database that organizes data into tables with rows and columns, allowing for relationships to be established between these tables. The tables in a relational database can be linked through primary and foreign keys, enabling complex queries and data manipulation across multiple tables.
What are primary and foreign keys in SQL?
A primary key is a column (or a combination of columns) in a table that uniquely identifies each row in that table. It is used to enforce data integrity and ensure that no duplicate records exist. A foreign key is a column (or a combination of columns) in a table that refers to the primary key of another table, establishing a relationship between the two tables. This allows for the enforcement of referential integrity, ensuring that data in related tables remains consistent.
Are there any limitations to using SQL?
While SQL is a powerful language for managing relational databases, it does have some limitations. These include:
- Limited support for handling complex data types like multimedia or geospatial data.
- Inability to perform complex calculations or process large datasets as efficiently as other programming languages.
- Differences in implementation and syntax across various database management systems (DBMS), which can lead to compatibility issues when switching between DBMS.
- Limited capabilities for handling concurrent users or transactions in some database systems.
Despite these limitations, SQL remains the most widely used language for relational database management due to its ease of use and widespread adoption.