---
title: "What is difference between COALESCE vs ISNULL in SQ Server?"  
description: "What is difference between COALESCE vs ISNULL in SQ Server?"  
author: "Ravi Vishwakarma"  
published: 2026-05-10  
updated: 2026-05-12  
canonical: https://answers.mindstick.com/qa/116580/what-is-difference-between-coalesce-vs-isnull-in-sq-server  
category: "database"  
tags: ["database", "sql server"]  
reading_time: 3 minutes  

---

# What is difference between COALESCE vs ISNULL in SQ Server?

**What is [difference](https://yourviews.mindstick.com/story/5016/chia-vs-basil-seeds-what-s-the-difference) between [COALESCE](https://www.mindstick.com/forum/159818/how-to-use-the-coalesce-function-to-handle-null-values-in-sql-queries) vs [ISNULL](https://www.mindstick.com/forum/162078/difference-between-coalesce-vs-isnull) in SQ [Server](https://www.mindstick.com/articles/43769/what-is-serverless-architecture-is-it-worth-switching-over)?**

## Answers

### Answer by Anubhav Sharma

In Microsoft SQL Server, both `COALESCE` and `ISNULL` are used to handle `NULL` values, but they differ in behavior, standards compliance, datatype handling, and flexibility.

## 1. Basic Syntax

## ISNULL

```plaintext
ISNULL(expression, replacement_value)
```

Example:

```plaintext
SELECT ISNULL(NULL, 'N/A');
```

Result:

```plaintext
N/A
```

## COALESCE

```plaintext
COALESCE(value1, value2, value3, ...)
```

Example:

```plaintext
SELECT COALESCE(NULL, NULL, 'N/A');
```

Result:

```plaintext
N/A
```

## 2. Main Differences

| Feature | ISNULL | COALESCE |
| --- | --- | --- |
| SQL Standard | No (SQL Server-specific) | Yes (ANSI SQL) |
| Number of arguments | 2 only | Multiple |
| Return datatype | Datatype of first argument | Highest precedence datatype |
| Evaluation | Function | Expression |
| Portability | Less portable | More portable |

## 3. Number of Arguments

## ISNULL → Only 2 values

```plaintext
ISNULL(value, replacement)
```

## COALESCE → Multiple values

```plaintext
COALESCE(value1, value2, value3, ...)
```

Example:

```plaintext
SELECT COALESCE(NULL, NULL, NULL, 'Default');
```

Very useful when checking several columns.

## 4. Datatype Handling (Important Difference)

## ISNULL returns datatype of FIRST argument

Example:

```plaintext
SELECT ISNULL(NULL, 1.5);
```

SQL Server may infer datatype unexpectedly depending on first argument.

Another example:

```plaintext
SELECT ISNULL(CAST(NULL AS VARCHAR(3)), 'ABCDEFG');
```

Result:

```plaintext
ABC
```

Because:

- first argument datatype = `VARCHAR(3)`
- replacement gets truncated

## COALESCE uses datatype precedence

Example:

```plaintext
SELECT COALESCE(CAST(NULL AS VARCHAR(3)), 'ABCDEFG');
```

Result:

```plaintext
ABCDEFG
```

This behavior is often safer and more intuitive.

## 5. ANSI Standard Compliance

## COALESCE

ANSI SQL standard

Works across many databases:

- SQL Server
- PostgreSQL
- Oracle
- MySQL

## ISNULL

- SQL Server-specific
- Not portable

## 6. Internal Behavior

`COALESCE` is internally translated into a `CASE` expression.

Equivalent:

```plaintext
COALESCE(a, b, c)
```

becomes roughly:

```plaintext
CASE
    WHEN a IS NOT NULL THEN a
    WHEN b IS NOT NULL THEN b
    ELSE c
END
```

## 7. Performance Difference

Usually:

- negligible difference
- both are fast in normal usage

Historically:

- `ISNULL` could be slightly faster in very specific cases
- modern SQL Server optimization makes this mostly irrelevant

## 8. When to Use Which?

## Use ISNULL when:

- You only need 2 arguments
- You want SQL Server-specific behavior
- You intentionally want first argument datatype

Example:

```plaintext
SELECT ISNULL(MiddleName, 'Not Provided')
FROM Employees;
```

## Use COALESCE when:

- You need multiple fallback values
- You want ANSI-standard SQL
- You want better portability
- You want datatype precedence handling

Example:

```plaintext
SELECT COALESCE(HomePhone, WorkPhone, MobilePhone, 'No Contact')
FROM Customers;
```

## 9. Common Interview Question

## Which is better?

Most developers prefer:

- `COALESCE` for portability and flexibility
- `ISNULL` for simple SQL Server-only replacements

A practical rule:

> Use `COALESCE` for standard, flexible SQL.\
> Use `ISNULL` for quick SQL Server-specific null replacement.

## Quick Summary

| Scenario | Recommended |
| --- | --- |
| ANSI-standard SQL | COALESCE |
| Multiple fallback values | COALESCE |
| Simple 2-value replacement | ISNULL |
| Predictable first-argument datatype | ISNULL |
| Cross-database compatibility | COALESCE |


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Original Source: https://answers.mindstick.com/qa/116580/what-is-difference-between-coalesce-vs-isnull-in-sq-server

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