topic Re: keep n join in QlikView

keep n join

Mon, 09 Feb 2015 10:01:54 GMT

when we use keep between two tables, the two tables will be kept as separate tables.

where as in join; they will be clubbed.

so, can we say that extra memory will be occupied in 1 st case and tat would degrade performance?

Re: keep n join

alexandros17 — Mon, 09 Feb 2015 10:05:09 GMT

Grom Help: take a look to the NOTE:

The keep prefix is similar to the Join prefix. Just as the join prefix, it compares the loaded table with an existing named table or the last previously created data table.

But instead of joining the loaded table with an existing table, it 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 comparison made is equivalent to a natural join made over all the common fields, i.e. the same way as in a corresponding join. However, the two tables are not joined and will be kept in QlikView as two separately named tables.

Note!
The explicit Join prefix 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 multiple tables instead of joining them, which greatly reduces memory usage, increases processing speed and offers enormous flexibility. Explicit joins should therefore generally be avoided in QlikView scripts. The keep functionality was designed to reduce the number of cases where explicit joins needs to be used.

Re: keep n join

kushalthakral — Mon, 09 Feb 2015 10:05:22 GMT

Dear Prudhvi

Actually we use keep whenever u need to track data as it will create two separate tables while in case of join it will store data in a single table so it would be difficult to track down the data.

Regards

Kushal T

Re: keep n join

Gysbert_Wassenaar — Mon, 09 Feb 2015 10:06:08 GMT

No, that conclusion doesn't automatically follow from that. Perhaps this blog post helps: A Myth about the Number of Hops

Re: keep n join

tresB — Mon, 09 Feb 2015 10:10:37 GMT

I like JohnW opinion here: http://community.qlik.com/message/13858#13858 in this regard.