1. Tally Function with Error Checking by Jeff Moden
Greased Lightning
Tally Function with Error Checking
by Jeff Moden
SPID Lightning Rounds, Detroit, Mi
12 September 2013

2. Your Speaker - Jeff Moden
17 years experience working with SQL Server
Mostly Self Taught
One of Leading Posters on SQLServerCentral.com
More than 33,000 posts (heh… some are even useful)
30+ articles on the “Black Arts” of T-SQL
Member since 2003
SQL Server MVP 2008 thru 2013
Winner of the “Exceptional DBA” award for 2011
Lead Application DBA, Data Architect, and SQL Mentor for Proctor Financial, Inc.
SQL Server is both my profession and my hobby
(Yeah, I know… I need to get a life ;-)
Tally Function with Error Checking
12 September 2013 © Copyright by Jeff Moden - All Rights Reserved

3. Agenda The Tally Function Error Checking in a Function
A high performance “readless” replacement for the Tally Table
Error Checking in a Function
How to check for and display meaningful errors from a function
Quick Demo of Performance and Error Messages
Tally Function with Error Checking
12 September 2013 © Copyright by Jeff Moden - All Rights Reserved

4. The Tally Function

5. Reference Material
Learn What a Tally Table/Function is and How It Replaces Certain Types of Loops:
How to Split Strings:

6. The Tally Function Tally Function with Error Checking
CREATE FUNCTION dbo.fnTally --===== Define the I/O for this function INT) RETURNS TABLE WITH SCHEMABINDING AS RETURN WITH --===== Generate up to 1 Million rows ("En" indicates the power of 10 produced) --E1(N) AS (SELECT 1 FROM (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1))n(N)), E1(N) AS (SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1), E3(N) AS (SELECT 1 FROM E1 a,E1 b,E1 c), E6(N) AS (SELECT 1 FROM E3 a,E3 b) --===== Conditionally start the sequence at 0 SELECT N = 0 = 0 UNION ALL --===== Enumerate the rows generated by the cascading CTEs (cCTE) SELECT TOP N = CAST(ROW_NUMBER()OVER(ORDER BY (SELECT N)) AS INT) FROM E6 ;
Explain why this is an “Inline” function and why that’s important for performance.
Explain how the “cascading CTE’s” work as a “row source”/”pseudo-cursor”.
Explain the difference between the commented out VALUES statement and E1.
Explain how the combination of ROW_NUMBER() and TOP produce values from 1
Explain how the SELECT N=0 works to start a sequence at 0 or 1.
Tally Function with Error Checking
12 September 2013 © Copyright by Jeff Moden - All Rights Reserved

7. Error Checking in a Function

8. Error Checking in a Function
CREATE FUNCTION dbo.fnTally --===== Define the I/O for this function INT) RETURNS TABLE WITH SCHEMABINDING AS RETURN WITH --===== Generate up to 1 Million rows ("En" indicates the power of 10 produced) --E1(N) AS (SELECT 1 FROM (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1))n(N)), E1(N) AS (SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1), E3(N) AS (SELECT 1 FROM E1 a,E1 b,E1 c), E6(N) AS (SELECT 1 FROM E3 a,E3 b) --===== Create understandable error messages if the parameters are incorrect. SELECT N = must be 0 or 1' AS INT) WHERE NOT BETWEEN 0 AND 1 UNION ALL SELECT N = must be between 0 and 1 Million' AS INT) > Negative values taken care of by TOP error --===== Conditionally start the sequence at 0 SELECT N = 0 = 0 --===== Enumerate the rows generated by the cascading CTEs (cCTE) SELECT TOP N = CAST(ROW_NUMBER()OVER(ORDER BY (SELECT N)) AS INT) FROM E6 ;
Explain that this is identical to the previous code (the function) with some added room.
Explain that RAISERROR and tradition error checking methods cannot be used.
When the error checking code comes on screen, explain the error checking message and conditions for each error check.
Tally Function with Error Checking
12 September 2013 © Copyright by Jeff Moden - All Rights Reserved

9. (See 01 fnTally with Error Checking.sql)
Quick Demo
(See 01 fnTally with Error Checking.sql)

10. Quick Review The Tally Function Error Checking in a Function
A high performance “readless” replacement for the Tally Table
Error Checking in a Function
How to check for and display meaningful errors from a function
Quick Demo of Performance and Error Messages
It’s real fast and the error messages help, but a real Tally Table is still faster.
Tally Function with Error Checking
12 September 2013 © Copyright by Jeff Moden - All Rights Reserved

11. See me at the end of tonight’s presentations.
Q’n’A
See me at the end of tonight’s presentations.
Tally Function with Error Checking
12 September 2013 © Copyright by Jeff Moden - All Rights Reserved

12. Tally Function with Error Checking by Jeff Moden
Greased Lightning
Tally Function with Error Checking
by Jeff Moden
Thanks for Listening
SPID Lightning Rounds, Detroit, Mi
12 September 2013