CAST/CONVERT makes expressions nullable

I came upon this issue when I was building some views to support legacy integrations to an app that I was refactoring. The view is supposed to have exactly the same column definitions as a table in the old database that I am redesigning, so to make SSIS packages and other integrations run smoothly, I want the view’s columns to have the same datatypes, nullability, etc.

But there are some gotchas to watch out for with CAST and CONVERT.

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Quick and dirty: How to right-align numeric columns in SSMS

Here are 50 random numbers:

--- 50 random numbers
WITH cte AS (
SELECT 0 AS i, 100000.*POWER(RAND(CHECKSUM(NEWID())), 3) AS n
UNION ALL
SELECT i+1, 100000.*POWER(RAND(CHECKSUM(NEWID())), 3)
FROM cte WHERE i<50)

SELECT *
FROM cte;

And in SSMS, with the variable-width default font, the output looks… slightly-less-than-readable in the grid view:

We could use STR() to format the output, but the indent looks a little off:

--- 50 random numbers
WITH cte AS (
SELECT 0 AS i, 100000.*POWER(RAND(CHECKSUM(NEWID())), 3) AS n
UNION ALL
SELECT i+1, 100000.*POWER(RAND(CHECKSUM(NEWID())), 3)
FROM cte WHERE i<50)

SELECT *, STR(n, 12, 2) AS with_str
FROM cte;

Here’s something I’ve found: the space character is roughly about half the width of a typical number character. So replace every leading space with two spaces, and it will look really neat in the grid:

--- 50 random numbers
WITH cte AS (
SELECT 0 AS i, 100000.*POWER(RAND(CHECKSUM(NEWID())), 3) AS n
UNION ALL
SELECT i+1, 100000.*POWER(RAND(CHECKSUM(NEWID())), 3)
FROM cte WHERE i<50)

SELECT *, STR(n, 12, 2) AS with_str,
       REPLACE(STR(n, 12, 2), ' ', '  ') AS with_replace
FROM cte;

(and terrible everywhere else, obviously.)

Grouping dates without blocking operators

It’s not entirely uncommon to want to group by a computed expression in an aggregation query. The trouble is, whenever you group by a computed expression, SQL Server considers the ordering of the data to be lost, and this will turn your buttery-smooth Stream Aggregate operation into a Hash Match (aggregate) or create a corrective Sort operation, both of which are blocking.

Is there anything we can do about this? Yes, sometimes, like when those computed expressions are YEAR() and MONTH(), there is. But you should probably get your nerd on for this one.

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