Notes for A.2.16 Methods to Construct a Query - IB | RevisionDojo
A.2.16 Methods to Construct a Query Notes
Constructing a query involves defining the criteria and logic that determine which data is retrieved from a database.
There are several methods to construct queries, ranging from graphical interfaces to structured query languages like SQL.
Graphical Query Builders
Graphical query builders provide a visual interface for constructing queries without writing code.
These tools are user-friendly and often used in applications like Microsoft Access.
Note
Graphical query builders are ideal for users who are not familiar with SQL or other query languages.
Steps to Construct a Query Using a Graphical Builder
Select Tables: Choose the tables from which to retrieve data.
Choose Fields: Select the specific fields to display in the results.
Set Criteria: Define conditions to filter the data (e.g., Age > 18).
Sort Results: Specify the order in which the results should be displayed.
Example
In Microsoft Access, you can use the Query Design view to selectfields like FirstName and LastName from a Students table and setcriteria such as Age > 18.
Structured Query Language (SQL)
SQL is the most widely used language for constructing queries in relational databases.
It allows for precise control over data retrieval and supports complex queries involving multiple tables.
Note
SQL queries are written using specific syntax and keywords, such as SELECT, FROM, WHERE, and JOIN.
Advanced SQL Features
Joins: Combine data from multiple tables.
Aggregations: Perform calculations like SUM, AVG, COUNT.
Subqueries: Use a query within another query to filter results.
Query by Example (QBE)
Query by Example (QBE) is a method where users fill out a template to define the query criteria.
The system then translates this template into a query language like SQL.
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Note
Introduction to Query Construction
Constructing a query involves defining the criteria and logic that determine which data is retrieved from a database.
There are several methods to construct queries, ranging from graphical interfaces to structured query languages like SQL.
DefinitionQueryA request for data or information from a database.
AnalogyThink of a query like a search filter on an online shopping website, where you specify what you're looking for, and the system retrieves matching items.
ExampleWhen you search for "red shoes size 10" on an e-commerce site, you're essentially constructing a query with specific criteria.
