November 14, 2012 at 9:00 am
Why does this delete all my records, reguardless of company?
delete Plant_Master
where EXISTS(Select Plant_CD from Plant_Master where company like 'MSC')
November 14, 2012 at 9:09 am
dwilliscp (11/14/2012)
Why does this delete all my records, reguardless of company?delete Plant_Master
where EXISTS(Select Plant_CD from Plant_Master where company like 'MSC')
does at least one row exist in Plant_Master where company = 'MSC'?
If so then EXISTS(Select Plant_CD from Plant_Master where company like 'MSC') evaluates to true and all records from Plant_Master are deleted.
If you want to delete records from Plant_Master where company = 'MCS' then you need to do :
delete Plant_Master
where company = 'MSC'
If you want to delete records from Plant_Master where company strats from 'MCS' then you need to do :
delete Plant_Master
where company LIKE 'MSC%'
If you want to delete records from Plant_Master where company contains 'MCS' then you need to do :
delete Plant_Master
where company LIKE '%MSC%'
November 14, 2012 at 12:25 pm
Hmm thought it would do a line by line check.. turns out that my thought process was off anyway. Given that we have data here that is not in SAP, I can not do any conditional deletes. I will have to use the update statement to update existing records, instead of deleting and re-loading.
However if the plan had not changed.. then the delete statement would still not have worked quite right. I still wonder how that would have worked. The idea was to have it select all records that existed and refresh only those... to get the list you would have to run the following SQL statement:
Select plant.Plant
from file_Plants as plant
left outer join Plant_Master as mas
on mas.Plant_CD = plant.Plant
where NOT(mas.Plant_CD is NULL)
November 14, 2012 at 12:37 pm
dwilliscp (11/14/2012)
Hmm thought it would do a line by line check.. turns out that my thought process was off anyway. Given that we have data here that is not in SAP, I can not do any conditional deletes. I will have to use the update statement to update existing records, instead of deleting and re-loading.However if the plan had not changed.. then the delete statement would still not have worked quite right. I still wonder how that would have worked. The idea was to have it select all records that existed and refresh only those... to get the list you would have to run the following SQL statement:
Select plant.Plant
from file_Plants as plant
left outer join Plant_Master as mas
on mas.Plant_CD = plant.Plant
where NOT(mas.Plant_CD is NULL)
Just my personal preference but I find this type of check to be far easier to read with a positive test.
where mas.Plant_CD IS NOT NULL
Of course in the case of this specific query why not just change the left join to an inner join since that is the result set you want to find. 😎
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November 14, 2012 at 12:59 pm
True, just a personal quirk. I find that when I am trying to think through something... I tend to code the thought process. Thus the outer join filtering where not NULL.
Sean Lange (11/14/2012)
dwilliscp (11/14/2012)
Hmm thought it would do a line by line check.. turns out that my thought process was off anyway. Given that we have data here that is not in SAP, I can not do any conditional deletes. I will have to use the update statement to update existing records, instead of deleting and re-loading.However if the plan had not changed.. then the delete statement would still not have worked quite right. I still wonder how that would have worked. The idea was to have it select all records that existed and refresh only those... to get the list you would have to run the following SQL statement:
Select plant.Plant
from file_Plants as plant
left outer join Plant_Master as mas
on mas.Plant_CD = plant.Plant
where NOT(mas.Plant_CD is NULL)
Just my personal preference but I find this type of check to be far easier to read with a positive test.
where mas.Plant_CD IS NOT NULL
Of course in the case of this specific query why not just change the left join to an inner join since that is the result set you want to find. 😎
November 14, 2012 at 3:46 pm
dwilliscp (11/14/2012)
True, just a personal quirk. I find that when I am trying to think through something... I tend to code the thought process. Thus the outer join filtering where not NULL.Sean Lange (11/14/2012)
dwilliscp (11/14/2012)
Hmm thought it would do a line by line check.. turns out that my thought process was off anyway. Given that we have data here that is not in SAP, I can not do any conditional deletes. I will have to use the update statement to update existing records, instead of deleting and re-loading.However if the plan had not changed.. then the delete statement would still not have worked quite right. I still wonder how that would have worked. The idea was to have it select all records that existed and refresh only those... to get the list you would have to run the following SQL statement:
Select plant.Plant
from file_Plants as plant
left outer join Plant_Master as mas
on mas.Plant_CD = plant.Plant
where NOT(mas.Plant_CD is NULL)
Just my personal preference but I find this type of check to be far easier to read with a positive test.
where mas.Plant_CD IS NOT NULL
Of course in the case of this specific query why not just change the left join to an inner join since that is the result set you want to find. 😎
I wouldn't call it "personal preference". It's wrong type of join, which can lead to worse performance.
That is exactly what INNER JOIN is for, so better to be written as
Select plant.Plant
from file_Plants as plant
inner join Plant_Master as mas
on mas.Plant_CD = plant.Plant
Now, as you select nothing from Plant_Master, you may find that the following will perform even better than INNER JOIN:
Select plant.Plant
from file_Plants as plant
where exists (select 1 from Plant_Master as mas
where mas.Plant_CD = plant.Plant)
Above two samples, can be actually called as "personal preference", but again, you may find that EXIST will give slightly better performance, as query processor will know that you need nothing from Plant_Master table.
November 15, 2012 at 8:17 am
Ok.. but how do you put that select logic into a delete statement?
November 15, 2012 at 8:36 am
dwilliscp (11/15/2012)
Ok.. but how do you put that select logic into a delete statement?
Change the word "select" to "delete".
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Understanding and Using APPLY (Part 2) - http://www.sqlservercentral.com/articles/APPLY/69954/
November 15, 2012 at 8:40 am
Eugene Elutin (11/14/2012)
I wouldn't call it "personal preference". It's wrong type of join, which can lead to worse performance.
That is exactly what INNER JOIN is for, so better to be written as
My preference I meant was to conditional check, I did point out that it should be an inner join.
The personal preference was to use
where mas.Plant_CD is NOT NULL
instead of
where NOT(mas.Plant_CD is NULL)
_______________________________________________________________
Need help? Help us help you.
Read the article at http://www.sqlservercentral.com/articles/Best+Practices/61537/ for best practices on asking questions.
Need to split a string? Try Jeff Modens splitter http://www.sqlservercentral.com/articles/Tally+Table/72993/.
Cross Tabs and Pivots, Part 1 – Converting Rows to Columns - http://www.sqlservercentral.com/articles/T-SQL/63681/
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs - http://www.sqlservercentral.com/articles/Crosstab/65048/
Understanding and Using APPLY (Part 1) - http://www.sqlservercentral.com/articles/APPLY/69953/
Understanding and Using APPLY (Part 2) - http://www.sqlservercentral.com/articles/APPLY/69954/
November 15, 2012 at 1:12 pm
Ok, thanks for the help 😀
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