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Category: Syntax

Set-Based Comparisons for Data Validation

Published 2025-05-12 by Kevin Feasel

Jeffry Schwartz looks for exceptions:

Given the complexity, I realized that validating all intermediate and final result sets was essential to ensure that tuning changes did not alter any report results.  To support this validation, I saved interim and final result sets into tables for direct comparison.

For these comparisons, the EXCEPT and INTERSECT operators proved invaluable. 

Click through for the full story. I’ve always liked using these set operations in ETL jobs because they automatically know how to handle NULL, so this approach is more robust than rigging your own comparisons.

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Working with the JSON Data Type in Azure SQL DB

Published 2025-05-08 by Kevin Feasel

Dennes Torres tries out the JSON data type in Azure SQL Database:

Before this new field type, JSON data was typically stored in varchar(max) columns. There are many features to use with JSON values stored in varchar(max) columns and variables, but storing JSON as regular strings is still limited.

The built-in JSON type expands the possibilities. Using an actual JSON column, it becomes easier to build constraints related to JSON columns, for example.

Dennes also spends a lot of the article covering the JSON_ARRAYAGG() and JSON_OBJECTAGG() functions.

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The APPLY Operator in T-SQL

Published 2025-05-07 by Kevin Feasel

I have a new video:

In this video, I explain the history behind the APPLY operator in T-SQL. I also demonstrate one use case for it: executing table-valued functions.

As I mention at the end of the video, this is by far the least interesting use case for the APPLY operator. Subsequent videos in the series get a lot more exciting. But we have to start at the beginning, unless we’re going full Pulp Fiction.

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Queue-Style Batch Deletion Woes in PostgreSQL

Published 2025-04-30 by Kevin Feasel

Shayon Mukherjee runs into an interesting issue:

I recently discovered an unexpected behavior in PostgreSQL involving a pattern of using a Common Table Expression (CTE) with DELETE ... RETURNING and LIMIT to process a batch of items from a queue-like table. What seemed straightforward turned out to have a surprising interaction with the query planner.

Click through to see what happened, as well as Shayon’s recommendation on how to fix it.

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Performing a Quick Filter via APPLY

Published 2025-04-28 by Kevin Feasel

Shane O’Neill tries something out:

Now, SQL Server doesn’t have the filter option, but we can do some pretty weird things, like a SELECT...WHERE statement with no FROM clause.

SELECT

    a,b,c,

    [filter?] = (SELECTb WHEREb > 11)

FROMz;

GO

It turns out that this works, but when you try to aggregate the results, it doesn’t work the way Shane expected. Using the APPLY operator does help here, so click through to see how that works.

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Session-Scoped Temp Tables in Microsoft Fabric now GA

Published 2025-04-23 by Kevin Feasel

Twinkle Cyril gets something GA:

Introducing distributed session-scoped temporary (#temp) tables in Fabric Data Warehouse and Fabric Lakehouse SQL Endpoints.

#temp tables have been a feature of Microsoft SQL Server (and other database systems) for many years. In the current implementation of Fabric data warehouse, #temp tables are session scoped or local temp tables. Global temp tables are not included in this release.

Session-scoped #temp tables exist only within the session in which they are created and last only for the duration of that session. They are not visible to other users or sessions and are automatically dropped from the system once the session ends or the user decides to drop the temp table. These tables are accessible to all users without requiring specific artifact-level permission.

Click through for examples of how it works and how you can specify a session-level temp table over a local temp table.

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The CHOOSE Function in SQL Server

Published 2025-04-22 by Kevin Feasel

Louis Davidson chooses the form of our destroyer:

I preface a lot of what I write with whether or not it is for a “practical” use. One of the Simple Talk authors used this function in a forthcoming article. and I realized I hadn’t heard of it before (or I forgot about it… which is not completely unlikely.) The practical use was to generate some data and have at least a little variety to the values.

The CHOOSE function has this syntax.

CHOOSE(item_to_choose, item1, item2 [,item3]…[itemN])

In fairness to Louis, CHOOSE() was one of those additions to SQL Server 2012 that we mostly forgot about. It’s similar in that vein to IIF() if you weren’t living in Excel at the time. In any event, Louis takes CHOOSE() through its paces, showing some useful scenarios and stretching the limits to see what happens.

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Hierarchy Management in PostgreSQL

Published 2025-04-18 by Kevin Feasel

Boris Novikov builds a list:

The Postgres database management system was originally designed as object-relational. We remind why PostgreSQL is an object-relational rather than just relational database management system, and briefly discuss what kind of object-oriented features it offers. We demonstrate how these features can be used to manage hierarchies, and how applications can benefit using them.

Click through for a technique native to PostgreSQL.

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Comparing INSERT INTO and SELECT * INTO

Published 2025-04-17 by Kevin Feasel

Haripriya Naidu runs an experiment:

Instead of looking at which option is faster, you may want to look at which option is better suited for a given context. Let’s take a look at 2 common options to insert data and analyze them.

INSERT INTO TARGETTABLE
SELECT * FROM SOURCETABLE

OR

SELECT * INTO TARGETTABLE 
FROM SOURCETABLE

Click through for a comparison of the two, not just for which is faster but also the pros and cons of each approach.

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