WEBVTT

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Review of SQL Basics

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Learning Objectives

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Recall and apply basic SQL commands like Select, Wear, Order, Buy and Limit.

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Modify data using Insert, Update and Delete safely.

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Summarize data using Count, Sum, AVG, MIN, Max, Group Buy and Having.

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Core SQL commands

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SQL, or Structured Query Language, is how we talk to databases.

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The most common command is Select, which fetches data from a table.

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For example, Select Star from Students. This shows us every single record.

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To filter these results, we use Wear. For example, the Query, Select Star from Students Wear, marks greater than 80.

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Retrieves only those students who scored more than 80 marks.

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Once we have retrieved the records from the students' table, we can arrange them in a specific order using the Order Buy clause.

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In the example shown, the data is sorted based on the Marks column.

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The Query, Select from Students Order by Marks ASC, arranges the students in ascending order, displaying them from the lowest marks to the highest.

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To keep things manageable, we use Limit command. This shows us just the top three rows.

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These core commands are your foundation for finding exactly the data you need.

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Data manipulation language

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Beyonds just reading data. SQL lets us modify it using DML commands.

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We use Insert to add brand new records.

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Insert into Students' Values. 6, John 11, 85, 6

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This adds a new student named John with Marks 85 in Class 6.

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We use Update to change existing data and table.

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Update student set Marks equals 85, where ID equals 2.

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Here, the marks of the student with ID 2 are updated to 85.

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And we use Delete to remove records we don't need from the existing table.

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Delete from Students where ID equals 6.

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This command deletes the student named John from the table.

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But here's the golden rule. Never, ever forget the wear clause in an update or delete.

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Without it, you might accidentally change or erase every single record in your table.

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Aggregate Functions

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SQL is also powerful for summarizing large amounts of information.

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We do this with aggregate functions.

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The key is the Group by Class ID line, which applies all these functions.

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Count, Sum, AVG, Max, and MN, separately to each class group.

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In the Select clause, we choose Class.ID, then use Count to get the number of students.

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Sum to calculate total marks and AVG for the average.

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We also use Max and MIN to find the highest and lowest scores in each class.

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Finally, the Having Clause filters the results to show only classes where the average marks are greater than 80,

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giving us just the high-performing groups for analysis.

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We learned how to retrieve data using Select and Wear.

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Organize it with Order Buy and Limit, modify tables using Insert, Update, and Delete,

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and summarize information with Count, Sum, AVG, MIN, Max, Group Buy, and Having.

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And of course, we saw why using the Wear Clause carefully helps avoid big mistakes.

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Master these simple tools and you'll be ready to handle real-world data smartly and safely.