Common Table Expression, why semicolon?

Question

Usually in SQL Server Common Table Expression clause there is semicolon in front of the statement, like this:

;WITH OrderedOrders AS --semicolon here
(
    SELECT SalesOrderID, OrderDate,
    ROW_NUMBER() OVER (ORDER BY OrderDate) AS 'RowNumber'
    FROM Sales.SalesOrderHeader 
) 
SELECT * 
FROM OrderedOrders 
WHERE RowNumber BETWEEN 50 AND 60

Why?

Solution

• To avoid ambiguity because WITH can be used elsewhere
  ..FROM..WITH (NOLOCK)..
RESTORE..WITH MOVE..
• It's optional to terminate statements with ; in SQL Server

Put together, the previous statement must be terminated before a WITH/CTE. To avoid errors, most folk use ;WITH because we don't know what is before the CTE

So

DECLARE @foo int;

WITH OrderedOrders AS
(
    SELECT SalesOrderID, OrderDate,
...;

is the same as

DECLARE @foo int

;WITH OrderedOrders AS
(
    SELECT SalesOrderID, OrderDate,
...;

The MERGE command has a similar requirement.

Comments

[Andriy M]

A quick and concise answer, very nice. Mine would take me either half a day long or half a mile page (slightly exaggerated, but not too much). The 'benefits' of speaking English as a second language...

[gotqn]

For newer versions - The SQL Server documentation indicates that not terminating T-SQL statements with a semicolon is a deprecated feature. This means that the long-term goal is to enforce use of the semicolon in a future version of the product. - Miscrosoft SQL Server 2012 T-SQL Fundamentals by Itzik Ben-Gan.

[Manngo]

Microsoft have deprecated the missing semicolon for over a decade, promising to require it in “a future version”. Good practice is always to use a terminating semicolon, just like all other databases. Among other things, this would remove the need for the quirky leading semicolon in this case.

[ZygD]

@Manngo agree, but sometimes it's just defensive programming especially in a shared dev environment