SQL Server Error 206

Error number

206

Severity

16 (user-correctable error)

State

2

Product

Microsoft SQL Server Database Engine

Versions

All supported SQL Server versions (2016 to 2025), Azure SQL Database, Azure SQL Managed Instance

Category

Data Type & Conversion

Last reviewed

24 October 2026

What it means

Error 206 means two values meet whose data types have no implicit conversion between them, such as an int sent to a date column, so SQL Server refuses to compile the statement.

Whenever a value is assigned, inserted, compared or combined with an operator, SQL Server needs both sides in one type. For most pairs it converts silently (int to decimal, varchar to date). For some pairs the conversion chart says no implicit conversion exists: int to date, int to uniqueidentifier, one table type to another. In those cases the batch stops with 206 at severity 16 and nothing runs. The message reads left to right as source is incompatible with target, so int is incompatible with date means an int was offered where a date is required.

Error 206 is about types, not values: it does not matter that 20261023 looks like a valid date. That is the difference from error 241 or error 245, which fire at run time when a conversion that is allowed meets a value it cannot read. The datetime2 trap is common after a migration: @d + 1 works on datetime but raises 206 on date, datetime2 and datetimeoffset.

Common causes

• An integer such as 20261023 inserted into, or compared with, a date or datetime2 column.
• Date arithmetic with + 1 or - 7 on date, datetime2 or datetimeoffset, which only datetime and smalldatetime support.
• A numeric value sent to a uniqueidentifier column, often because the INSERT column list and the VALUES list are in different orders.
• A table-valued parameter declared with a different table type than the procedure expects, even when both types have the same columns.
• A procedure parameter changed from int to date (or the reverse) while callers still pass the old type.

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 c.name AS column_name, t.name AS data_type
FROM sys.columns AS c
JOIN sys.types AS t ON t.user_type_id = c.user_type_id
WHERE c.object_id = OBJECT_ID(N'dbo.Bookings')
ORDER BY c.column_id;

EXEC sp_describe_first_result_set
     N'SELECT DATEADD(day, 1, CAST(''2026-10-23T09:00'' AS datetime2)) AS next_day;';

SELECT p.name AS parameter_name,
       SCHEMA_NAME(tt.schema_id) + N'.' + tt.name AS table_type,
       p.is_readonly
FROM sys.parameters AS p
JOIN sys.table_types AS tt ON tt.user_type_id = p.user_type_id
WHERE p.object_id = OBJECT_ID(N'dbo.CancelOrders');

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.

DECLARE @due datetime2 = '2026-10-23T09:00';
SELECT DATEADD(day, 1, @due) AS next_day;

INSERT INTO dbo.Bookings (id, booked_on)
VALUES (1, CONVERT(date, CAST(20261023 AS char(8)), 112));

DECLARE @ids dbo.OrderIdList;
INSERT INTO @ids (order_id) VALUES (101), (102);
EXEC dbo.CancelOrders @ids = @ids;

INSERT INTO dbo.Sessions (session_id, user_id)
VALUES (NEWID(), 42);

Examples

An integer date inserted into a date column

CREATE TABLE dbo.Bookings (id INT PRIMARY KEY, booked_on DATE);

INSERT INTO dbo.Bookings (id, booked_on) VALUES (1, 20261023);  -- an int, not a date

Msg 206, Level 16, State 2, Line 3
Operand type clash: int is incompatible with date

Adding a day to a datetime2 with + 1

DECLARE @due datetime2 = '2026-10-23T09:00';
SELECT @due + 1 AS next_day;  -- works for datetime, not for datetime2

Msg 206, Level 16, State 2, Line 2
Operand type clash: datetime2 is incompatible with int

A table-valued parameter with an identical but different type

CREATE TYPE dbo.OrderIdList AS TABLE (order_id INT);
CREATE TYPE dbo.IdList AS TABLE (order_id INT);  -- same columns, different type
GO
CREATE PROCEDURE dbo.CancelOrders @ids dbo.OrderIdList READONLY
AS SELECT order_id FROM @ids;
GO
DECLARE @ids dbo.IdList;
EXEC dbo.CancelOrders @ids = @ids;

Msg 206, Level 16, State 2, Procedure dbo.CancelOrders, Line 0
Operand type clash: IdList is incompatible with OrderIdList

How to prevent it

Keep values in their real types end to end: dates as date or datetime2 parameters, identifiers as uniqueidentifier, and avoid integer or text stand-ins. Write date arithmetic with DATEADD and DATEDIFF from the start, so a later change from datetime to datetime2 does not break it.

Define each table type once and reuse it for every procedure that takes the same list. For which types convert implicitly and which never do, see SQL data types explained and the conversion chart in the CAST and CONVERT reference.

Common questions

Learn more on CodeWithSQL

• DATEADD()
• CONVERT()
• SQL data types explained

Official documentation

• CAST and CONVERT (Transact-SQL)
• Data type conversion (Database Engine)
• Use table-valued parameters (Database Engine)
• Database Engine events and errors 0 to 999

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.