Chapter 2 Supplement
Correlated Subqueries
© Spring 2012 Imelda Go, John Grego, Jennifer Lasecki and the University of South Carolina
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Example – Correlated Subquery
AtBats
Playerposition
Player
Atbats
Player
Position
Walker
271
Marzilli
Outfield
Wingo
240
Williams
Outfield
Thomas
231
Bradley Jr.
Outfield
Marzilli
220
Wingo
Infield
Beary
211
Walker
Infield
Morales
249
Thomas
Infield
Mooney
254
Marzilli
Infield
Williams
209
Morales
Infield
Bradley Jr.
162
Mooney
Infield
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Correlated Subqueries

In Chapter 2, we saw one example of a
correlated subquery:
proc sql;
select player, atbats from atbats
where "Infield"= (select position
from playerposition where
atbats.player=playerposition.playe
r); quit;
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Example Correlated Subquery
Step 1 – The outer query takes the first row in
atbats table and finds the columns player and
atbats.
 Step 2 – Match atbats.player (passed from table
in outer query) with playerposition.player to find
the qualifying row in the playerposition table.
 Step 3 – The inner query now passes the
position of the selected row in playerposition
back to the outer query via the = operator,
where the position is matched for the selection
in the outer query.

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Example – Correlated Subquery
Player
Atbats
Walker
271
Wingo
240
Thomas
231
Beary
211
Morales
249
Mooney
254
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Example-Correlated Subquery
Correlated subqueries suggest that SAS
has the ability to resolve ambiguous
references.
 Regardless, when creating code, we often
get error messages that look like:
ERROR: Unresolved reference to
table/correlation name varname

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Example-Correlated Subquery

We can modify the correlated subquery so
that
- The reference to playerposition.player
is less clear
- playerposition.player is not even
selected in the outer query, but does appear
in the referenced data set (atbats)
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