SQL Server Error 8624

Error number

8624

Severity

16 (user-correctable error)

State

Not documented by Microsoft (not reproduced here)

Product

Microsoft SQL Server Database Engine

Versions

All supported SQL Server versions (2016 to 2025), Azure SQL Database, Azure SQL Managed Instance; specific to the query shape and build

Category

Query Processing & Performance

Last reviewed

24 October 2026

What it means

Error 8624 means the Query Optimizer hit an internal problem while building a plan for one statement; it points to a product defect for that query shape, not to a mistake in your data.

Every statement is compiled into a plan before it runs. With 8624 the compilation fails inside the query processor itself: the optimiser reached a state it should never reach, gave up, and asks you to contact Microsoft support. Nothing runs, so no data is changed, and other statements on the instance are not affected. The same statement fails every time it is compiled on that build, which makes the problem reproducible for you even though it is a defect in the product.

Do not confuse it with 8622 (your hints make a plan impossible) or 8623 (the statement is too complex to optimise). 8624 is the "internal error" member of this family: the practical answers are to find the exact statement, check whether a cumulative update fixes it, and change the query shape so that it compiles in the meantime.

Common causes

• A defect in the query processor for a particular combination of query features (for example complex views, nested subqueries, computed columns, indexed views or unusual join patterns).
• A build that lacks a cumulative update containing the fix for that defect.
• A change of database compatibility level or optimiser setting that sends the statement down a different, faulty optimisation path.
• A statement generated by a tool or ORM in an unusual shape that hand-written queries rarely produce.

Diagnose it

Read-only These queries only read metadata and dynamic management views. They do not change data, permissions or configuration, so they are safe to run first.

SELECT SERVERPROPERTY('ProductVersion') AS product_version,
       SERVERPROPERTY('ProductLevel') AS product_level,
       SERVERPROPERTY('ProductUpdateLevel') AS update_level,
       SERVERPROPERTY('ProductUpdateReference') AS update_kb,
       SERVERPROPERTY('Edition') AS edition;

SELECT name, compatibility_level
FROM sys.databases
WHERE database_id = DB_ID();

SELECT name, value
FROM sys.database_scoped_configurations
WHERE name IN (N'QUERY_OPTIMIZER_HOTFIXES', N'LEGACY_CARDINALITY_ESTIMATION');

SELECT p.plan_id, p.query_id, p.is_forced_plan,
       p.force_failure_count, p.last_force_failure_reason_desc
FROM sys.query_store_plan AS p
WHERE p.is_forced_plan = 1;

How to fix it

Each fix is labelled with what it changes. Try read-only checks and the least invasive fix first, and test changes outside production.

-- Instead of one large statement, stage the first step
SELECT o.customer_id, SUM(o.total) AS total_spent
INTO #spend
FROM dbo.Orders AS o
GROUP BY o.customer_id;

SELECT c.name, s.total_spent
FROM dbo.Customers AS c
JOIN #spend AS s ON s.customer_id = c.customer_id;

SELECT c.name, SUM(o.total) AS total_spent
FROM dbo.Customers AS c
JOIN dbo.Orders AS o ON o.customer_id = c.customer_id
GROUP BY c.name
OPTION (USE HINT ('QUERY_OPTIMIZER_COMPATIBILITY_LEVEL_150'));

Examples

A statement fails at compile time on an affected build

Shown as documented in the engine message catalogue; not reproduced here. 8624 depends on a defect in a specific build for a specific query shape, and no such repro is known for the current build, so the query below only illustrates where the error appears. The level and state were not observed, so no header is shown.

SELECT c.name, SUM(o.total) AS total_spent
FROM dbo.Customers AS c
JOIN dbo.Orders AS o ON o.customer_id = c.customer_id
GROUP BY c.name;

Internal Query Processor Error: The query processor could not produce a query plan. For more information, contact Customer Support Services.

How to prevent it

Stay current with cumulative updates, and test them, so that known optimiser defects are fixed before you meet them. Test compatibility level changes against your real workload (Query Store makes before and after comparisons easy) before switching production.

Keep very large generated statements in check: queries built in simpler steps are easier for the optimiser and for people to reason about. See the advanced query optimisation lesson.

Common questions

Learn more on CodeWithSQL

• Advanced query optimisation
• Performance tuning

Official documentation

• Database engine events and errors 8000 to 8999
• Latest updates for Microsoft SQL Server
• Query hints (Transact-SQL)

Last technically reviewed 24 October 2026; examples and diagnostics run on SQL Server 2025 (17.0.1145.4). Message text checked against the engine's sys.messages catalogue.