Guaranteed Easy! Here's How to Use Subquery in SQL for Beginners!

Use SQL (Structured Query Language) to manage databases is a highly valuable skill in today's digital world. One of the important concepts in SQL is subquery or inner query, which allows you to construct complex queries more efficiently. For those of you who are just starting to learn SQL, this article will discuss how to use subqueries easily, so you can put it into practice immediately.

Subquery is a query that is inside another query. Usually, subqueries are used to retrieve temporary data that will be further processed by the main query. Subqueries can be placed in the SELECT, WHERE, or FROM sections of a SQL query. By using subqueries, you can simplify and optimize the process of searching for data in the database.

Subqueries are very useful when:

• You need to filter data based on the results of other queries.
• you want to do calculation or grouping data first before running the main query.
• You have to compare mark from different tables without doing complicated joins.

How to Use Subqueries in SQL

1. Subquery in SELECT to Add Data Columns

Using subqueries in sections SELECT allows you to add additional data into results displayed by the main query. This is especially useful if you want to include calculation results or other information that is not directly available in the main table. Subquery placed in SELECT will generate data for each row of the main table, and those results will then be displayed as additional columns in the final results.

2. Subquery in WHERE to Filter Data

Using subqueries in sections WHERE very useful when you need to filter data from the main table based on the results of another query. This way, you can narrow down the data retrieved by the main query based only on the conditions met by the subquery. Subquery in WHERE usually used to retrieve the value of or list the value to be compared with the data in the main table.

3. Subquery in FROM to Create Temporary Table

Using subqueries in sections FROM allows you to create temporary table or virtual table which can then be processed further by the main query. This subquery functions as a new data source that seems to be an additional table in the main query. Technique This is useful when you want to perform grouping or calculations that need to be processed further in subsequent queries, so you can simplify complex query structures.

Tips and Tricks for Using Subqueries for Data Analysts

• Avoid using unnecessary subqueries because they can slow down query performance.
• Before creating a subquery, make sure you understand the relationships between inner tables database.
• Subquery can help you in doing data analysis more complex ones, such as calculating the average value or finding the maximum value in a particular dataset.

Subquery is one of the most useful tools in SQL. By mastering the use of subqueries, you can simplify the data analysis process and get more accurate results. Although the subquery can be visible complicated At first, with practice and good understanding, you will soon get used to it and be able to use it in various situations.

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