Public Checklist: SQL Practical Checklist

Set up SQL environment

Install a database server and client tools to start practicing SQL.

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Install a SQL database server (e.g., PostgreSQL, MySQL)

Download the installer for your OS, follow the setup wizard, and ensure the service is running.

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Install a SQL client/application (e.g., DBeaver, Azure Data Studio)

Choose a GUI client that supports your database, install it, and create a connection profile.

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Create a sample database and load demo data

Use the client to create a new database (e.g., 'learnsql') and import a sample schema like Sakila or Northwind for practice.

Learn basic SELECT queries

Understand how to retrieve data from tables using SELECT statements.

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Select all columns from a table

Use SELECT * FROM table_name; to view every column and row.

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Select specific columns

List column names after SELECT to return only needed data, e.g., SELECT first_name, last_name FROM employees;

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Use column and table aliases

Assign temporary names with AS for readability, e.g., SELECT e.first_name AS fname FROM employees e;

Filter data with WHERE and sort results

Combine WHERE clauses for filtering and ORDER BY for sorting.

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Apply comparison operators (=, <>, >, <, >=, <=)

Filter rows where column values meet specific conditions, e.g., WHERE salary > 50000;

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Combine conditions with AND and OR

Use AND to require multiple conditions, OR to satisfy any of them, e.g., WHERE department = 'Sales' AND region = 'North';

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Filter ranges with BETWEEN and list values with IN

Use BETWEEN for inclusive ranges, IN for matching any value from a list, e.g., WHERE age BETWEEN 20 AND 30;

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Sort results with ORDER BY (ASC/DESC) and multiple columns

Order output ascending or descending, add multiple columns for tie-breaking, e.g., ORDER BY last_name ASC, first_name DESC;

Aggregate data with GROUP BY and HAVING

Summarize data using aggregate functions and filter groups.

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Use aggregate functions COUNT, SUM, AVG, MIN, MAX

Calculate totals, averages, and extremes, e.g., SELECT COUNT(*) AS total_orders FROM orders;

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Group by a single column

Aggregate rows sharing the same value in a column, e.g., SELECT department, AVG(salary) FROM employees GROUP BY department;

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Group by multiple columns

Create finer groupings, e.g., SELECT department, job_title, AVG(salary) FROM employees GROUP BY department, job_title;

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Filter groups with HAVING clause

Apply conditions on aggregated results, e.g., HAVING AVG(salary) > 60000;

Join tables to combine related data

Learn different join types to query data across multiple tables.

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Understand inner join concept

Returns rows when there is a match in both tables; the most common join.

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Write an INNER JOIN query

Syntax: SELECT columns FROM table1 INNER JOIN table2 ON table1.id = table2.foreign_id;

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Write a LEFT (OUTER) JOIN query

Returns all rows from left table and matched rows from right; unmatched right columns are NULL.

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Write a RIGHT (OUTER) JOIN query

Returns all rows from right table and matched rows from left; unmatched left columns are NULL.

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Join on multiple conditions and use table aliases

Combine several AND conditions in ON clause and alias tables for brevity, e.g., ON a.id = b.a_id AND a.status = 'active';

Modify data and follow best practices

Insert, update, delete data safely and apply performance & security tips.

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Insert a single row with INSERT INTO ... VALUES

Add one record, specifying values for each column or omitting columns with defaults.

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Insert multiple rows at once

Provide several value sets separated by commas, e.g., INSERT INTO table (col1,col2) VALUES (1,'A'), (2,'B');

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Insert data from another table (INSERT INTO ... SELECT)

Copy rows from one table to another, optionally transforming data.

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Update existing rows with UPDATE ... SET

Modify column values, always include a WHERE clause to limit rows unless intending to update all.

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Delete rows safely with DELETE FROM ... WHERE

Remove specific rows; consider using a transaction and checking rows affected before committing.