Case Statement Short-Circuiting

Richie Lee talks about using the CASE statement to short-circuit a logical expression:

The issue here is that SQL is a declarative language: unlike procedural languages, there is no guarantee on the ordering of the operations, because optimizers. And SQL Server decides to do something other than what we’d expect: it tries to evaluate the value “Apu” as a date. But by using a CASE expression we can force the optimizer to take the input and match it to the expression (in this case, when a value is a date then convert it to a date) before checking if the value is older than 7 days.

This does work most of the time, but there are exceptions, so as always, test your code.

Related Posts

Validating SSIS Packages Using T-SQL

Annie Xu shows us how to validate SSIS packages in the SSISDB catalog using T-SQL: Recently, I need to do a data warehouse migration for a client. Since there might be some difference between the Dev environment source databases and Prod environment source databases. The migrated SSIS packages for building data warehouse might have some […]

Read More

APPROX_COUNT_DISTINCT

Niko Neugebauer is happy with a new function in SQL Server 2019: A rather interesting result takes place if we scale our database to 100GB TPCH and run the very same queries – the total elapsed time jumps to 50% difference (from 30%), the CPU execution time difference is kept at 50%, but the memory […]

Read More

Categories

January 2016
MTWTFSS
« Dec Feb »
 123
45678910
11121314151617
18192021222324
25262728293031