---
title: "How do you identify missing indexes?"  
description: "How do you identify missing indexes?"  
author: "ICSM Computer"  
published: 2026-05-15  
updated: 2026-05-15  
canonical: https://www.mindstick.com/interview/34512/how-do-you-identify-missing-indexes  
category: "database"  
tags: ["database", "sql server"]  
reading_time: 5 minutes  

---

# How do you identify missing indexes?

Indexes are essential for improving query performance in SQL Server. When indexes are missing, SQL Server may perform full table scans, causing slow queries, high CPU usage, and increased I/O operations. Identifying missing indexes is an important part of database performance tuning.

## 1. Using Execution Plans

The easiest way to identify missing indexes is through the **Actual Execution Plan** in SQL Server Management Studio (SSMS).

Enable it using:

```plaintext
Ctrl + M
```

Then execute your query:

```plaintext
SELECT *
FROM Orders
WHERE CustomerID = 1001;
```

SQL Server may display a green message like:

```plaintext
Missing Index (Impact 85%)
```

It also suggests a recommended index:

```plaintext
CREATE NONCLUSTERED INDEX IX_Orders_CustomerID
ON Orders(CustomerID);
```

This indicates that adding an index on `CustomerID` could significantly improve performance.

## 2. Using Missing Index DMVs

SQL Server stores missing index recommendations in Dynamic Management Views (DMVs).

Use this query:

```plaintext
SELECT
    migs.avg_user_impact,
    mid.statement AS TableName,
    mid.equality_columns,
    mid.included_columns
FROM sys.dm_db_missing_index_groups mig
JOIN sys.dm_db_missing_index_group_stats migs
    ON mig.index_group_handle = migs.group_handle
JOIN sys.dm_db_missing_index_details mid
    ON mig.index_handle = mid.index_handle
ORDER BY migs.avg_user_impact DESC;
```

This shows:

- table name
- suggested columns
- estimated improvement percentage

Higher `avg_user_impact` means higher performance benefit.

## 3. Analyze Table Scans

If execution plans show:

- Table Scan
- Clustered Index Scan

instead of:

- Index Seek
- it often indicates missing indexes.

Example:

```plaintext
SELECT OrderID, Amount
FROM Orders
WHERE OrderDate = '2026-05-01';
```

Without an index, SQL Server scans the entire table.

Solution:

```plaintext
CREATE NONCLUSTERED INDEX IX_Orders_OrderDate
ON Orders(OrderDate);
```

This allows SQL Server to use an efficient Index Seek.

## 4. Use Query Store

SQL Server Query Store helps identify slow and expensive queries over time. Queries with high reads or CPU usage often need better indexing.

## Best Practices

- Do not create every suggested index blindly.
- Too many indexes slow down INSERT, UPDATE, and DELETE operations.
- Combine similar indexes when possible.
- Use INCLUDE columns for covering indexes.
- Monitor performance after index creation.

Example:

```plaintext
CREATE NONCLUSTERED INDEX IX_Orders
ON Orders(CustomerID)
INCLUDE (OrderDate, Amount);
```

## Conclusion

Missing indexes can severely affect SQL Server performance. They can be identified using:

Execution Plans

- DMVs
- Query Store
- Table Scan analysis

Proper indexing improves query speed, reduces I/O, and enhances overall database performance. However, indexes should always be tested and optimized carefully to avoid unnecessary overhead.

## Answers

### Answer by ICSM Computer

Indexes are essential for improving query performance in SQL Server. When indexes are missing, SQL Server may perform full table scans, causing slow queries, high CPU usage, and increased I/O operations. Identifying missing indexes is an important part of database performance tuning.

## 1. Using Execution Plans

The easiest way to identify missing indexes is through the **Actual Execution Plan** in SQL Server Management Studio (SSMS).

Enable it using:

```plaintext
Ctrl + M
```

Then execute your query:

```plaintext
SELECT *
FROM Orders
WHERE CustomerID = 1001;
```

SQL Server may display a green message like:

```plaintext
Missing Index (Impact 85%)
```

It also suggests a recommended index:

```plaintext
CREATE NONCLUSTERED INDEX IX_Orders_CustomerID
ON Orders(CustomerID);
```

This indicates that adding an index on `CustomerID` could significantly improve performance.

## 2. Using Missing Index DMVs

SQL Server stores missing index recommendations in Dynamic Management Views (DMVs).

Use this query:

```plaintext
SELECT
    migs.avg_user_impact,
    mid.statement AS TableName,
    mid.equality_columns,
    mid.included_columns
FROM sys.dm_db_missing_index_groups mig
JOIN sys.dm_db_missing_index_group_stats migs
    ON mig.index_group_handle = migs.group_handle
JOIN sys.dm_db_missing_index_details mid
    ON mig.index_handle = mid.index_handle
ORDER BY migs.avg_user_impact DESC;
```

This shows:

- table name
- suggested columns
- estimated improvement percentage

Higher `avg_user_impact` means higher performance benefit.

## 3. Analyze Table Scans

If execution plans show:

- Table Scan
- Clustered Index Scan

instead of:

- Index Seek
- it often indicates missing indexes.

Example:

```plaintext
SELECT OrderID, Amount
FROM Orders
WHERE OrderDate = '2026-05-01';
```

Without an index, SQL Server scans the entire table.

Solution:

```plaintext
CREATE NONCLUSTERED INDEX IX_Orders_OrderDate
ON Orders(OrderDate);
```

This allows SQL Server to use an efficient Index Seek.

## 4. Use Query Store

SQL Server Query Store helps identify slow and expensive queries over time. Queries with high reads or CPU usage often need better indexing.

## Best Practices

- Do not create every suggested index blindly.
- Too many indexes slow down INSERT, UPDATE, and DELETE operations.
- Combine similar indexes when possible.
- Use INCLUDE columns for covering indexes.
- Monitor performance after index creation.

Example:

```plaintext
CREATE NONCLUSTERED INDEX IX_Orders
ON Orders(CustomerID)
INCLUDE (OrderDate, Amount);
```

## Conclusion

Missing indexes can severely affect SQL Server performance. They can be identified using:

Execution Plans

- DMVs
- Query Store
- Table Scan analysis

Proper indexing improves query speed, reduces I/O, and enhances overall database performance. However, indexes should always be tested and optimized carefully to avoid unnecessary overhead.


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