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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Exercise 2: Solution<br />
<strong>select</strong> salary,<br />
salary*2 as doubleSalary<br />
from employee<br />
where branch = ‘Glasgow' or<br />
branch = ‘London'<br />
salary<br />
64<br />
44<br />
64<br />
doubleSalary<br />
128<br />
88<br />
128<br />
19<br />
Selection, Projection, and Jo<strong>in</strong><br />
• Us<strong>in</strong>g <strong>select</strong> statements with a s<strong>in</strong>gle relation <strong>in</strong> the<br />
from clause we can realise:<br />
– <strong>select</strong>ions,<br />
– projections,<br />
– renam<strong>in</strong>gs<br />
• Jo<strong>in</strong>s (and Cartesian products) are realised by us<strong>in</strong>g two<br />
or more relations <strong>in</strong> the from clause<br />
20
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