Always Use Semicolon Statement Terminators

ANSI-standard semicolon statement terminators are often omitted in T-SQL queries and many developers are unaware that this is syntax is deprecated.  Omitting statement terminators is a dangerous practice because, even if the batch compiles, you may get unexpected results.  Consider the insidious examples below pointed out by SQL Server MVP Erland Sommarskog:

BEGIN TRY
	BEGIN TRAN
	SELECT 1/0 AS CauseAnException
	COMMIT
END TRY
BEGIN CATCH
	SELECT ERROR_MESSAGE()
	THROW
END CATCH

Few of us will catch (no pun intended) the bug in the above script.  What results do you expect after running the above script under SQL Server 2012 or later versions?  Rather than leave this as an exercise for the reader, I’ll spoil the fun and mention that no run-time error is raised at all.  Instead, the THROW statement is interpreted as a column alias for the ERROR_MESSAGE() column.  This sort of coding error is especially nasty because catch blocks are rarely unit tested and this catch block coding mistake hides the run-time error entirely without raising an exception.

Similarly, the absence of statement terminators in the script below causes another problem.  Can you spot it?

BEGIN TRY
	BEGIN TRAN
	SELECT 1/0 AS CauseAnException
	COMMIT
END TRY
BEGIN CATCH
    IF @@TRANCOUNT > 0 ROLLBACK TRAN
    THROW
END CATCH

At least an error is raised in this case, albeit not the one you might expect.  The resultant error is “Cannot roll back THROW. No transaction or savepoint of that name was found”.  This coding bug obfuscates the preceding divide by zero error and prevents the THROW statement from being executed.

Semicolons Will Become Mandatory
Microsoft announced with the SQL Server 2008 release that semicolon statement terminators will become mandatory in a future version so statement terminators other than semicolons (whitespace) are currently deprecated.  This deprecation announcement means that you should always use semicolon terminators in new development.  I honestly don’t expect SQL Server to strictly enforce mandatory semicolons in the near future but it is still a best practice to use semicolon statement to avoid issues like those mentioned earlier as well as facilitate code maintainability.  I suggest specifying statement terminators in all new development and perhaps adding terminators to existing code as you perform maintenance.

Transact-SQL does not currently enforce the ANSI semicolon statement terminator requirement.  Instead, semicolon statement terminators are optional and any whitespace (spaces, tabs, newline) may be used instead.  The exception to this rule is that many of the statements introduced in SQL Server 2005 and later require the preceding statement to be properly terminated in order for the batch to compile.

Below are some guidelines I suggest on when to, and when not to, use semicolon statement terminators.

Suggested Guidelines
The Transact-SQL parser is quite lax, allowing any whitespace (e.g. space, tab, newline) to be used.  This laxness results in ambiguity like the examples at the beginning of this article demonstrate.  Similarly, statement terminators may not only be omitted, they may also be used in inappropriately.  I strongly suggest you adhere to the T-SQL syntax documented in the Books Online even if the parser allows otherwise.  This practice will help future-proof your code since relying on undocumented behavior is inherently risky.

Don’t precede a statement with a semicolon
Remember that the purpose of semicolons is to terminate SQL statements, not begin them.  A common mistake I see is throwing a semicolon in front of statements in order to get a batch of statements to compile, especially with newer statements like WITH (CTE expression) that require previous statement termination.  Although the T-SQL parser currently ignores extraneous and misplaced semi-colons, I suggest they be specified in the appropriate place according statement syntax documented in the SQL Server Books Online.

Specify semicolons at the end of each stand-alone SQL statement
Not only will this conform to the ANSI standard, your intent will be clearer and the code easier to read.

Terminate control-of-flow statement blocks at the end of the control-of-flow scope
Control-of-flow statements are not covered by the ANSI SQL standard because these are proprietary SQL extensions.  The SQL Server Books Online is sketchy on the subject and many of the examples (as of this writing) are inconsistent and do not always include statement terminators.  Furthermore, control-of-flow statement blocks are confusing due to the many variations, nesting, and optional BEGIN/END specifications.

Below are examples illustrating what I believe to be proper use of statement terminators control-of-flow block terminators using IF statements in SQL 2008 and later versions.  The same concepts apply to other control-of-flow constructs like WHILE and TRY/CATCH blocks.  I should add that this batch example will not compile under SQL 2005 because an explicit BEGIN/END block is required to execute a common table expression conditionally in that version.  T-SQL parser enhancements eliminated that requirement in SQL 2008 and later.

IF 1 = 1
  WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement and IF

IF 1 = 1
  WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
ELSE
  WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement and IF

IF 1 = 1
  BEGIN
    WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
  END; --terminate IF

IF 1 = 1
  BEGIN
    WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
  END
ELSE
  BEGIN
    WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
  END; --terminate IF

IF 1 = 1
  WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
ELSE
  BEGIN
    WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
  END; --terminate IF

IF 1 = 1
  BEGIN
    WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
  END
ELSE
  WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement and IF

IF 1 = 1
  BEGIN
    WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
	IF 1 = 1
		WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
	ELSE
	BEGIN
		WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
	END; --terminate inner nested IF
	WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement
  END
ELSE
  WITH a AS (SELECT 1 a) SELECT a FROM a; --terminate statement and outer IF

Summary
Consistent user of semicolons helps avoid bugs in code that might otherwise go undetected.  Code with statement terminators can also be more easily modified without introducing compile errors and make code easier to maintain because the end of each statement is readily apparent to subsequent developers.  Importantly, you’ll be better positioned for future SQL Server versions by consistently using semicolon statement terminators.