Introduction to Database Systems Queries in SQL The select ...
Introduction to Database Systems Queries in SQL The select ...
Introduction to Database Systems Queries in SQL The select ...
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Correlated Subqueries<br />
It may be necessary <strong>to</strong> use <strong>in</strong> <strong>in</strong>ner blocks variables that are<br />
def<strong>in</strong>ed <strong>in</strong> outer blocks. In this case one talks about correlated<br />
subqueries.<br />
Example: <strong>The</strong> fathers all of whose children earn strictly more than<br />
20k.<br />
<strong>select</strong> dist<strong>in</strong>ct fc.father<br />
from fatherChild fc<br />
where not exists (<strong>select</strong> *<br />
from fatherChild fc0, person c<br />
where fc.father = fc0.father<br />
and fc0.child = c.name<br />
and c.<strong>in</strong>come
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