Correlated Subqueries

Chapter 2 Supplement

1© Spring 2012 Imelda Go, John Grego, Jennifer Lasecki and the University of South

Carolina

Example – Correlated Subquery

Player Atbats

Walker 271

Wingo 240

Thomas 231

Marzilli 220

Beary 211

Morales 249

Mooney 254

Williams 209

Bradley Jr.

162

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Player Position

Marzilli Outfield

Williams Outfield

Bradley Jr. Outfield

Wingo Infield

Walker Infield

Thomas Infield

Marzilli Infield

Morales Infield

Mooney Infield

AtBatsPlayerposition

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.player); 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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