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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for June 26th, 2018

SQL: “where not exists … having” formulation; anti-join alternative

Posted by jpluimers on 2018/06/26

I need to write up some notes, but there are some links that will help me:

It’s a question of readability. There is no difference in performance.
Old versions of SQL Server were silly enough to look up meta data, but not any more.

SELECT foo FROM bar WHERE EXISTS (SELECT * FROM baz WHERE baz.id = bar.id);
SELECT foo FROM bar WHERE EXISTS (SELECT 1 FROM baz WHERE baz.id = bar.id);

I am not considering NULL or “fun variants” which don’t seem intuitive to me.

SELECT foo FROM bar WHERE EXISTS (SELECT NULL FROM baz WHERE baz.id = bar.id);

SELECT foo FROM bar WHERE EXISTS (SELECT 1/0 FROM baz WHERE baz.id = bar.id);

The question popped up in comments just now. I researched the manuals of the most popular RDBMS:

A search on SO for code:"EXISTS (SELECT 1" yields 5,048 results.
A search on SO for code:"EXISTS (SELECT *" yields 5,154 results.
Updated links and counts 07.2015.

So SELECT * has the popular vote and the big commercial RDBMS on its side.
I find SELECT 1 more intuitive. It’s like saying “if at least one exists”.
Is SELECT * more intuitive?

–jeroen

 

 

Posted in Database Development, Development, Firebird, InterBase, MySQL, PostgreSQL, SQL, SQL Server | Leave a Comment »

A Programmer’s Introduction to Unicode – Nathan Reed’s coding blog

Posted by jpluimers on 2018/06/26

Must read if you do i18n or l10n: [WayBackA Programmer’s Introduction to Unicode – Nathan Reed’s coding blog

Via:

[WayBack] Even if you’ve been programming with Unicode for years, this well-written article is worth reading. – Kevin Powick – Google+

–jeroen

 

Posted in Development, internatiolanization (i18n) and localization (l10), Software Development | Leave a Comment »

Settings Migration Tool – RAD Studio

Posted by jpluimers on 2018/06/26

I totally missed that this was introduced in Delphi XE8: [Archive.isSettings Migration Tool – RAD Studio.

It allows exporting/importing your Delphi settings and migrate them from older Delphi versions.

I need to try to find out which older Delphi versions it supports.

–jeroen

via: [WayBack] For once, I remembered …\Studio\19.0\bin\migrationtool.exe and imported all the IDE tweaks and color settings I had… – Lars Fosdal – Google+

Read the rest of this entry »

Posted in Delphi, Development, Software Development | 4 Comments »

 
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