Understanding Join, Keep and Concatenate

[#1]

We have implemented the QlikView Join, Keep and Concatenate in QvScriptor, a new revolutionary tool, able to generate QlikView script from visual schema.

We have written this small doc for the help file and we thing interesting to share it with the community as we found only partial explanations about the methods.

The QlikView script functions JOIN, KEEP and CONCATENATE can sometimes be used to solve the same problem, but there are important differences that should be understood.

Examine the sample tables below. Note that they share one common field name, "Key".

Also note that Table1 has a Key value "3" that is not present in Table2 and that Table2 has a key 4 that is not present in Table1.

Table1			Table2
Key	A		Key	C
1	A1		1	C1
2	A2		2	C2
3	A3
			4	C4

Type of Joins:

JOIN will combine rows where the Key value matches.

• The keyword OUTER will also retain rows that do not match rows in the other table.
• The keyword LEFT will retain rows from the left table but only matching rows from the right table
• The keyword RIGHT will retain rows from the right table but only matching rows from the left table
• The keyword INNER will retain rows matching the left table and right table

Joins

Here's what the merged table will look like after the different join methods.

Note that QlikView merge the two tables after a Join.

Note: The explicit join keyword (= Outer Join) in QlikView script language performs a full join of the two tables. The result is one table. In many cases such joins will result in very large tables. One of the main features of QlikView is its ability to make associations between tables instead of joining them, which greatly reduces memory usage, increases processing speed and offers enormous flexibility. Explicit joins should therefore be generally avoided in QlikView scripts. The keep functionality was designed to reduce the number of cases where you need to use explicit joins

OUTER JOIN (Table1)				LEFT JOIN (Table1)
Key	A	C		Key	A	C
1	A1	C1		1	A1	C1
2	A2	C2		2	A2	C2
3	A3	-		3	A3	-
4	-	C4

RIGHT JOIN (Table1)				INNER JOIN (Table1)
Key	A	C		Key	A	C
1	A1	C1		1	A1	C1
2	A2	C2		2	A2	C2
4	-	C4

Keep

The keep prefix between two load or select statements has the effect of reducing one or both of the two tables before they are stored in QlikView, based on the intersection of table data. The keep keyword must always be preceded by one of the prefixes inner,left or right. The selection of records from the tables is made in the same way as in a corresponding join.

However, the two tables are not joined and will be stored in QlikView as two separately named tables.

LEFT KEEP
Table1			Table2
Key	A		Key	C
1	A1		1	C1
2	A2		2	C2
3	A3		3	-

RIGHT KEEP
Table1			Table2
Key	A		Key	C
1	A1		1	C1
2	A2		2	C2
4	-		4	C4

INNER KEEP
Table1			Table2
Key	A		Key	C
1	A1		1	C1
2	A2		2	C2

Concatenate

Now let's look at Concatenate. Concatenate appends the rows of one table to another. Concatenate never merges any rows. The number of rows in a concatenated table is always the sum of the rows from the two input tables. Here's what our sample data will look like after Concatenate.

CONCATENATE (Table1) LOAD * RESIDENT Table2;

Key	A	C
1	A1
1		C1
2	A2
2		C2
3	A3
4		C4

Rows with like Key values are not merged together. The rows from Table2 are simply appended to Table1. Because the tables have different fields, rows will have null values for the fields from the "other" table.

QsGen Team

[montubhardwaj]

Good one. Thanks.

[Anonymous]

Thank you very much.
Would it be possible for you to add the respective statements that are used?

I am trying to get familiarised with the statement nomenclature.

[sanketkhunte]

Hi Friends,

Thank you for your Time.

Here I would like to ask one question regarding JOIN in QlikView.

Let say I have 2 facts : Fact_One and Fact_Two

In Fact_One there are few fields like : SegmentID1,SegmentID2,SegmentID3,SegmentID4.

and

in Fact_Two there is only one field for this mapping field is SEG_ID

Now My requirement is that How Can i join these two facts in Qlik View data model which satisfy :

if Control not find value in SegmentID1 of Fact_One table then it will goes to SegmentID2 and if control not finds match then this will go to SegmentID3 and all WITH SEG_ID

Your answer will appriciate me.

Regards

Sanket Khunte

[#5]

You cam make 4 subsequents loads

1) Fact_One.SegmentID1 INNERJOIN Fact_Two.SEG_ID

2) Fact_One.SegmentID2 INNERJOIN Fact_Two.SEG_ID

3) Fact_One.SegmentID3 INNERJOIN Fact_Two.SEG_ID

4) Fact_One.SegmentID4 INNERJOIN Fact_Two.SEG_ID

Hope this help

[vikasmahajan]

Informative...

vikas

[sanketkhunte]

Thank you John.

[#8]

Good explaination.

I have one more question. Can I have a Left Join & Left Keep in the same Load statement.

Eg.

Left Keep (ABC)

Left Join (XYZ)

Load

  E, F, G

From OPQ.QVD(qvd);

[#9]

Vinod,

I am not sure that syntax that you mention would work.

But yes, disparate Join/keep statement followed with respective Load statement would work.

Regards,

SK

[ashwanin]

Nice .One of the best ppt in explanation.

[#11]

thanks, i have seen many papers on joins  .. this one is so far the best papers on joins ...