Why doesn't a trailing comma after the last field matter when creating a table using T-SQL?

Question

Shouldn't one of these statements work and one fail?

Intuition says Statement 2 should fail because there is a comma after int and no second column listed.

Yet both work and the trailing comma "," after the last column data type makes no difference.

-- Statement 1
CREATE TABLE dbo.MyTable1( col1 int);

-- Statement 2
CREATE TABLE dbo.MyTable2( col1 int,);

However (and this is expected): two commas ",," after the last field do cause a failure:

-- Statement 3
CREATE TABLE dbo.MyTable3( col1 int,,);

Msg 102, Level 15, State 1, Line 1
Incorrect syntax near ','.

Testing shows that its not just any character after the last field that is allowed through. For example, this fails:

-- Statement 3
CREATE TABLE dbo.MyTable3( col1 int ~);

Msg 102, Level 15, State 1, Line 1
Incorrect syntax near '~'.

Maybe SQL Server is "saving a seat at the table" for something? The Primary Key perhaps? I really don't know.

I am using Microsoft SQL Server 2008 R2 (SP1) - 10.50.2500.0 (X64).

Answer 1

See http://connect.microsoft.com/SQLServer/feedback/details/273348/trailing-comma-allowed-in-create-table:

Description

When executing the CREATE TABLE command, a trailing comma following the last column is allowed. Based on the grammar in BOL and comma usage in lists in other T-SQL statements, this behavior is inconsistent. This is a very minor issue and does not appear to cause any adverse side-effects. It just appears that the parser may be a bit off.

Microsoft views this as a bug, but a minor one.

This was resolved some time ago as "won't fix" but we didn't explain why. Simply, this seems pretty harmless, and not worth fixing in a service pack. We may consider fixing this in a future release.

Answer 2

Almost all languages which permit comma-separated list items permit a comma after the last list item. This is done to make editing the program or file, and especially inserting new list items, easier. You don't have to worry about adding a comma after the current last list item, or removing a comma if you delete the old last list item.