---
title: "Why does DeepSeek’s SQL omit customers with no recent orders?"  
description: "Why does DeepSeek’s SQL omit customers with no recent orders?"  
author: "Khoa Vu"  
published: 2026-10-17  
updated: 2026-10-17  
canonical: https://www.mindstick.com/forum/162550/why-does-deepseek-s-sql-omit-customers-with-no-recent-orders  
category: "PostgreSQL Query Debugging"  
tags: ["DeepSeek", "postgresql", "SQL Debugging", "AI-Generated Code"]  
reading_time: 1 minute  

---

# Why does DeepSeek’s SQL omit customers with no recent orders?

I asked DeepSeek for a PostgreSQL query that lists every customer and counts their orders placed on or after January 1, 2026. Customers with no qualifying orders should still appear with a count of zero.

This is the query I’m checking:

```sql
SELECT
    c.id,
    c.name,
    COUNT(o.id) AS order_count
FROM customers AS c
-- Keep customers in the join even when no order matches.
LEFT JOIN orders AS o
    ON o.customer_id = c.id
-- Restrict the report to orders from the requested period.
WHERE o.created_at >= DATE '2026-01-01'
GROUP BY c.id, c.name;
```

In my three-customer test, one customer has a recent order, one has only an older order, and one has never ordered. Only the first customer appears, although I expected three rows.

I thought the **LEFT JOIN filtering behavior** would preserve all customers. Is the date condition changing that, and does it matter whether the condition belongs in `ON` or `WHERE`?

I’d also like to understand **COUNT with unmatched rows**. If I get DeepSeek to revise the query, should I keep `COUNT(o.id)`, or would `COUNT(*)` produce the same zero-order result? I’m looking for the reasoning so I can review similar generated queries myself.


---

Original Source: https://www.mindstick.com/forum/162550/why-does-deepseek-s-sql-omit-customers-with-no-recent-orders

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