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3 weeks ago

My question is about the select statement and its usage.

Following is the code used to calculate average, i copied it from base sas codes avaiable online to understand function but can't understand why does it have "e. and d.". and what does it mean to say "class e class d",

Also need to understand the calcuation highlighted [in bold].

Step 1 : Creating Data set

data class;

set sashelp.class;

obs = _n_;

run;

Step 2 : Proc Sql

proc sql;

select avg(weight) as Median

from (select** e.**weight

from **class e, class d**

group by **e.**weight**having sum(case when e.weight = d.weight then 1 else 0 end)****>= abs(sum(sign(e.weight - d.weight))));**

quit;

Thanks !

Accepted Solutions

Solution

3 weeks ago

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3 weeks ago

Firstly e and d are aliases i.e. they are ways of referring to different variables in different data sets. In this particular case e and d both refer to the same data set and what is being produced is a cartesian product i.e. a data set which contains all possible combinations of weights (the table is being joined with itself).

The highlighted code is basically a complicated way of finding the median (i.e. the value with the same number of observations which are greater than it and which are less than it) by using the sum of differences. If you're using SAS 9.4 you can simply do this instead

```
proc sql;
select median(weight)
from class;
quit;
```

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3 weeks ago

It may contribute to your understanding to know that you could just as well write

`from class as e, class as d`

e and d are simply the names you are using to refference you datasets, so you can refference them by

```
select avg(weight) as Median
from (select e.weight
```

Solution

3 weeks ago

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3 weeks ago

Firstly e and d are aliases i.e. they are ways of referring to different variables in different data sets. In this particular case e and d both refer to the same data set and what is being produced is a cartesian product i.e. a data set which contains all possible combinations of weights (the table is being joined with itself).

The highlighted code is basically a complicated way of finding the median (i.e. the value with the same number of observations which are greater than it and which are less than it) by using the sum of differences. If you're using SAS 9.4 you can simply do this instead

```
proc sql;
select median(weight)
from class;
quit;
```

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3 weeks ago

Thanks

It worked when I used SAS 9.4.