Re: Need some help with SQL case/when performance

On Feb 25, 2021, at 1:14 PM, Charles Wilt <charles.wilt@xxxxxxxxx> wrote:

quite possibly...

Indexes (especially unique) on the source file? and none on the output
file?

Most definitely that would cause UPDATE to be slower than READ from one
WRITE to another.

Without seeing your actual SQL, the RPG code and the details of the files,
I can only speculate.

But I can say you've either done something wrong or are comparing apples to
oranges if the SQL took 12hrs and RPG took 20min.

Charles


On Thu, Feb 25, 2021 at 11:06 AM <smith5646midrange@xxxxxxxxx> wrote:

Are you saying it is slower to update the same location than to write
somewhere else? That doesn't make since to me.


-----Original Message-----
From: MIDRANGE-L <midrange-l-bounces@xxxxxxxxxxxxxxxxxx> On Behalf Of John
Yeung
Sent: Thursday, February 25, 2021 12:56 PM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxxxxxxxx>
Subject: Re: Need some help with SQL case/when performance

On Thu, Feb 25, 2021 at 12:47 PM <smith5646midrange@xxxxxxxxx> wrote:

I don't understand why it would be different.

The SQL is one read to get the data and one write to update the data.
The RPG is one read to get the data and one write to write the data.

There's a potentially huge difference between reading something at one
location and then writing to the same location, versus reading at one
location and writing to another location.

John Y.
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