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Structured Query Language
SQL Meaning
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SQL (Structured Query Language) is a specialized programming language designed for managing and manipulating data stored in relational databases. It allows users to perform various operations such as querying, updating, inserting, and deleting data efficiently
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Key Principles of SQL
Declarative Language: SQL is a declarative language, meaning it specifies what data to retrieve or manipulate rather than how to perform the operation. This makes it easier to use and understand
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Standardization: SQL became a standard of the American National Standards Institute (ANSI) in 1986 and the International Organization for Standardization (ISO) in 1987
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Components: SQL consists of several sublanguages, including Data Query Language (DQL), Data Definition Language (DDL), Data Control Language (DCL), and Data Manipulation Language (DML)
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Common SQL Commands
SELECT: Retrieves data from a database.
INSERT: Adds new records to a database.
UPDATE: Modifies existing records.
DELETE: Removes records from a database.
CREATE: Creates new database objects like tables and views.
ALTER: Modifies existing database objects.
DROP: Deletes database objects
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Example of a Simple SQL Query
SELECT * FROM Customers WHERE CustomerName LIKE 'J%' ORDER BY CustomerID DESC LIMIT 10;
This query retrieves the top 10 customers whose names start with 'J', ordered in descending order by their customer ID
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Uses of SQL
SQL is widely used across various industries and applications, including:
Data Retrieval: Extracting data from databases for analysis and reporting.
Data Manipulation: Adding, updating, and deleting data in databases.
Data Definition: Defining the structure and organization of data in databases.
Access Control: Managing user permissions and ensuring data security
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Important Considerations
Interoperability: SQL implementations can vary between different database systems, leading to compatibility issues
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Security: SQL injection is a common security vulnerability where malicious SQL code is inserted into queries to manipulate or corrupt data
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In conclusion, SQL is a powerful and versatile language for managing relational databases, offering a wide range of functionalities for data manipulation, retrieval, and security
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Harlow is a town and local government district located in the west of Essex, England. Founded as a new town, it is situated on the border with Hertfordshire, and occupies a large area of land on the south bank of the upper Stort Valley, which has been made navigable through other towns and features a canal section near its watermill.
Old Harlow is a historic village founded by the early medieval age and most of its high street buildings are early Victorian and residential, mostly protected by one of the Conservation Areas in the district. In Old Harlow is a field named Harlowbury, a de-settled monastic area which has the remains of a chapel, a scheduled ancient monument. The M11 motorway passes through to the east of the town. Harlow has its own commercial and leisure economy. It is also an outer part of the London commuter belt and employment centre of the M11 corridor which includes Cambridge and London Stansted Airport to the north.
At the time of the 2011 Census, Harlow's population was recorded at 81,944 and its district had the third-highest proportion of social housing in England, 26.9%,[citation needed] a legacy of the 1947 commitment to re-house blitzed London families after World War II and provide a percentage of homes for other needy families who cannot afford market rents.
