OVER (PARTITION BY ORDER BY )
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Hello everyone, I'm trying to understand this function. Someone wrote this piece of code and I would like to use to do something simular. On a daily basis we read .txt files into our SQL database through SSIS. The data that's going through is growing fast and takes a long time to process. (for example a year of data is read every day into the db) I want to make a dayset so that we only read one single day into the DB on top of the existing data and not the whole year. Someone wrote this peace of code:
Select * , ROW_NUMBER() OVER (PARTITION BY PK_Assignment ORDER BY DATE, TIME) as LineNbr
from ProductivityColliDagSetI was wondering what the Partition By statement means. My guess was that you have to place the fields there that makes the record unique. Can someone help me out with this because I read so many things on the internet and still I don't understand. Also I don't have much experience with SQL, just the basics. Ambertje
It determines the grouping. Play around with below script;
BEGIN TRANSACTION
CREATE TABLE SomeTest( Field1 INTEGER, Field2 CHAR(1), Data VARCHAR(50)) INSERT INTO SomeTest VALUES (1, 'C', 'Test') INSERT INTO SomeTest VALUES (1, 'A', 'Test') INSERT INTO SomeTest VALUES (7, 'C', 'Test') INSERT INTO SomeTest VALUES (7, 'A', 'Test') INSERT INTO SomeTest VALUES (4, 'C', 'Test') SELECT \* , ROW\_NUMBER() OVER ( PARTITION BY Field2 ORDER BY Field1 ) FROM SomeTestROLLBACK
If you change the field that's being partitioned by to "Field1", you'll see a different grouping in the result-set (with each group receiving a unique numbering). It's often used with a primary key because some idiot forgot to add an identity-field :)
Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]
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It determines the grouping. Play around with below script;
BEGIN TRANSACTION
CREATE TABLE SomeTest( Field1 INTEGER, Field2 CHAR(1), Data VARCHAR(50)) INSERT INTO SomeTest VALUES (1, 'C', 'Test') INSERT INTO SomeTest VALUES (1, 'A', 'Test') INSERT INTO SomeTest VALUES (7, 'C', 'Test') INSERT INTO SomeTest VALUES (7, 'A', 'Test') INSERT INTO SomeTest VALUES (4, 'C', 'Test') SELECT \* , ROW\_NUMBER() OVER ( PARTITION BY Field2 ORDER BY Field1 ) FROM SomeTestROLLBACK
If you change the field that's being partitioned by to "Field1", you'll see a different grouping in the result-set (with each group receiving a unique numbering). It's often used with a primary key because some idiot forgot to add an identity-field :)
Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]
Eddy Vluggen wrote:
some idiot forgot to added an identity-field
FTFY
You'll never get very far if all you do is follow instructions.
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Eddy Vluggen wrote:
some idiot forgot to added an identity-field
FTFY
You'll never get very far if all you do is follow instructions.
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Real databases use a sequence. ;-)
Wrong is evil and must be defeated. - Jeff Ello[^]
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Hello everyone, I'm trying to understand this function. Someone wrote this piece of code and I would like to use to do something simular. On a daily basis we read .txt files into our SQL database through SSIS. The data that's going through is growing fast and takes a long time to process. (for example a year of data is read every day into the db) I want to make a dayset so that we only read one single day into the DB on top of the existing data and not the whole year. Someone wrote this peace of code:
Select * , ROW_NUMBER() OVER (PARTITION BY PK_Assignment ORDER BY DATE, TIME) as LineNbr
from ProductivityColliDagSetI was wondering what the Partition By statement means. My guess was that you have to place the fields there that makes the record unique. Can someone help me out with this because I read so many things on the internet and still I don't understand. Also I don't have much experience with SQL, just the basics. Ambertje
Ambertje wrote:
I want to make a dayset so that we only read one single day into the DB on top of the existing data and not the whole year.
I don't see what that has to do with partitions - the database of course wouldn't have anything to do with reading files.
Ambertje wrote:
and takes a long time to process.
Someone should optimize that process. I wouldn't be surprised if that means moving it out of SSIS but maybe it can be sped up as is. Normally one profiles a process by actually timing the various parts and then using that data to determine where things can be made faster. Although your description might suggest that every day you read the previous years data. If so one obvious optimization there would be to some producing a file that has a years worth of data. How one does that depends on the data.
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Real databases use a sequence. ;-)
Wrong is evil and must be defeated. - Jeff Ello[^]
Begone with your Oracle concepts bah humbug!
Never underestimate the power of human stupidity RAH
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Hello everyone, I'm trying to understand this function. Someone wrote this piece of code and I would like to use to do something simular. On a daily basis we read .txt files into our SQL database through SSIS. The data that's going through is growing fast and takes a long time to process. (for example a year of data is read every day into the db) I want to make a dayset so that we only read one single day into the DB on top of the existing data and not the whole year. Someone wrote this peace of code:
Select * , ROW_NUMBER() OVER (PARTITION BY PK_Assignment ORDER BY DATE, TIME) as LineNbr
from ProductivityColliDagSetI was wondering what the Partition By statement means. My guess was that you have to place the fields there that makes the record unique. Can someone help me out with this because I read so many things on the internet and still I don't understand. Also I don't have much experience with SQL, just the basics. Ambertje
The best way to understand this is to create a couple of tables and experiment. It is quite difficult to explain what is going on in a partition statement - the closest I can get is transposing data in Excel. However that does not explain how to go about transposing the data. Think of it as changing column headings into row contents and row contents into column headings.
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
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It determines the grouping. Play around with below script;
BEGIN TRANSACTION
CREATE TABLE SomeTest( Field1 INTEGER, Field2 CHAR(1), Data VARCHAR(50)) INSERT INTO SomeTest VALUES (1, 'C', 'Test') INSERT INTO SomeTest VALUES (1, 'A', 'Test') INSERT INTO SomeTest VALUES (7, 'C', 'Test') INSERT INTO SomeTest VALUES (7, 'A', 'Test') INSERT INTO SomeTest VALUES (4, 'C', 'Test') SELECT \* , ROW\_NUMBER() OVER ( PARTITION BY Field2 ORDER BY Field1 ) FROM SomeTestROLLBACK
If you change the field that's being partitioned by to "Field1", you'll see a different grouping in the result-set (with each group receiving a unique numbering). It's often used with a primary key because some idiot forgot to add an identity-field :)
Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]
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The best way to understand this is to create a couple of tables and experiment. It is quite difficult to explain what is going on in a partition statement - the closest I can get is transposing data in Excel. However that does not explain how to go about transposing the data. Think of it as changing column headings into row contents and row contents into column headings.
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
-
Begone with your Oracle concepts bah humbug!
Never underestimate the power of human stupidity RAH
:)
Wrong is evil and must be defeated. - Jeff Ello[^]