SQL Indexing — Complete Guide

SQL Indexing — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of ADO.NET Core Tutorial on Toolliyo Academy.

8 min read Updated 8/21/2026

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ADO.NET Core Tutorial · Lesson 44 of 100

SQL Indexing

Foundations ✓ → SQL & safety → Production → Projects

SQL & safety · 2 — Procs, tx, performance · ~6 min · Module 5: Performance Optimization

What is this?

Indexes speed WHERE/ORDER BY at write cost — create them for real ShopNest predicates.

Why should you care?

Without indexes, parameterized queries still scan.

See it live — copy this example

Use a .NET console or API project with SQL Server LocalDB. Run dotnet run after pasting.

CREATE INDEX IX_Orders_CustomerId_Id
ON Orders(CustomerId, Id DESC)
INCLUDE (Total, Status);

What happened?

Composite order matters.
INCLUDE covers selected columns.
Don’t index every column.

Practice next

Create the index.
Re-run history query plan.
Check write impact lightly.
Filtered index WHERE Status=Pending.
Rebuild online in prod carefully.

Remember

Index real filters. INCLUDE for covering. Balance writes.

ShopNest history index

IX_Orders_CustomerId_Id added.

Outcome: Account history p95 drops.

Interview prep for this lesson

Practice these questions aloud after reading—each links to a full structured answer.

Junior PDF Detailed

What is ADO.NET?

Short answer: ADO.NET (Active Data Objects .NET) is a data access technology in the .NET framework that enables applications to interact with databases and other data sources. Explain a bit more It provides a set of clas…

Mid PDF Detailed

Memory Efficiency:?

Short answer: A DataReader is a forward-only, read-only cursor, meaning it streams data from the database and does not store the entire result set in memory. DataSet, on the other hand, loads the entire result set into m…

Mid PDF Detailed

Optimistic Concurrency Control:?

Short answer: Optimistic Concurrency assumes that conflicts will be rare and allows multiple users to read and modify data without locking it. Explain a bit more When updating data, you compare the current data in the da…

Mid PDF Detailed

Using ExecuteReader (for a single row, multiple columns):?

Short answer: SqlCommand command = new SqlCommand("SELECT CustomerName, ContactName FROM Customers WHERE CustomerID = @CustomerID", connection); command.Parameters.AddWithValue("@CustomerID", 1); conn…

Mid PDF Detailed

SqlCommand: Used for SQL Server databases. It represents a Transact-SQL?

Short answer: command or stored procedure. Example: SqlCommand command = new SqlCommand("SELECT * FROM Customers", connection); Example code command or stored procedure. Example: SqlCommand command = new SqlCom…

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