This function is widely used in Excel, SQL, etc. In the context of QlikView, concatenate refers to the concatenation of rows where this function helps to append the rows from one table to another. It is important for us to understand this difference before we study further into the Concatenate function in QlikView. The Concatenate function in QlikView is used to append the rows from one table to another.
This command will function even if the number of fields in the two tables does not match or if the fields in the two tables are not identical. The concatenation takes place automatically if the tables have identical field names. When the field names are not identical, we force the Concatenate function to do the job. The Concatenate and Concat are both available in QlikView. It is good to know the difference between their functions so that we do not get confused later.
The Concatenate is used in the script, whereas the Concat is used in expressions as well as rarely used in the script. This is an automatic function in QlikView where the concatenation of two or more loaded tables will automatically occur when the number of fields and the names of the fields of the tables are similar.
This will result in the concatenation of the different statements into a single table. This is a manual concatenation method that is done using the script. Forced concatenation is done when the number of fields and the names of the fields differ between the loaded tables. This enables us to concatenate a table with another named table or with the previously created table. Not so fast, grasshopper! In our recent experience, we were healing a troubled dataset built by someone else, who clearly never attended the Masters Summit.
One Fact table of approximately Million rows was linked to another Fact table of approximately Million rows, and various measures were scattered among various Dimension tables. Our first reaction was — we need to build a Star schema! Getting ahead, we can proudly say that we saw more than a tenfold improvement of performance as a result of this brief data modeling exercise. Anyway, in the process of concatenating the Facts into a single Fact table, we noticed that the LOAD that performed the concatenation worked extremely slowly, compared to other LOAD statements.
It was even slower than the statement that joined data from the two huge Fact tables. That caught our attention, and we decided to monitor the process more closely. This discovery seems illogical, but our results suggested just that. And yes, we are aware of the specifics of each command and the differences in their functionality.
The JOIN load will attempt to match identical key fields. If the two joining tables have no identical keys, the join becomes a Cartesian Join, which is certainly undesired.
When there are identical fields, they are used as Join keys, and for each matching set of keys, a joined row will get created. So, our goal is to ensure that the two tables share at least one identical field, and that there are no matching sets of key values.
When the data from one Fact is marked with one Fact Type and the data from another Fact is marked with another Fact Type, then surely no matching keys will ever exist! So, our simple work around that saves a lot of load time, schematically looks like the following:. We could include the most valuable insights in our next session of Masters Summit for QlikView once again, look to the right!
Good idea to use an outer join for concatenation. Hmm, interesting idea — to prepare both loads for automatic concatenation I assume, by adding all the missing fields on both sides. Sounds like a lot of extra handling, however it might be worth the trouble for huge data sets. Maybe, this can be automated by a sub where one dummy record without data is loaded from both tables with concatenate just to create an empty table upfront with all fields..
Thanks for the post! How does this change if we consider optimized loads? I have a case where I concatenate two similar tables and the second is tweaked so that it loads optimized.
As I understand it the load is not optimized when joining. Does it make sense to change to join? Thank you for your question. I never compared the load times between the optimized concatenated load and a join load. In most cases, qlik view developers will need to lay out instructions for qlik view to follow concatenation performance. Qlik view calls this forced concatenation, and it is necessary when the tables that have to be combined do not have the same number or names of columns. A forced concatenation is done using the concatenate prefix before load in the script.
This will concatenate the table following the concatenate statement to the table created immediately before this statement. Because we did not specify the table name to concatenate it to in the concatenate statement concatenate table name is the best practice , the statement appends the rows from electronics. Csv onto the last table created TOYS.
The number of records in the resulting table is the sum of the number of records in TOYS. The value of product-name in the records coming from electronics.
0コメント