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Category Archives: SQL
🞑 Can test whether a nested query generates any duplicate tuples 🞑 UNIQUE (...) 🞑 NOT UNIQUE (...) 🞑Not widely implemented 🞑 Expensive…
¨ Example: “Find branches with assets greater than all branches in Brooklyn.” SELECT branch_name FROM branch WHERE assets > ALL ( SELECT assets…
¨ General form of test: attr compare_op SOME ( subquery ) 🞑 Can use any comparison operation = SOME is same as IN…
¨ Can compare a value to a set of values 🞑 Is a value larger/smaller/etc. than some value in the set? ¨ Example:…
¨ Many correlated subqueries can be restated using a join or a Cartesian product 🞑 Often the join operation will be much faster…
“Find customers with an account but not a loan.” SELECT DISTINCT customer_name FROM depositor d WHERE NOT EXISTS ( SELECT * FROM borrower…
“Find customers with an account but not a loan.” SELECT DISTINCT customer_name FROM depositor d WHERE NOT EXISTS ( SELECT * FROM borrower…
¨ Can test whether or not a subquery generates any results at all EXISTS (...) NOT EXISTS (...) ¨ Example: “Find customers with…
IN (...) and NOT IN (...) support subqueries that return multiple columns (!!!) ¨ Example: “Find the ID of the largest loan at…
Can use IN (...) and NOT IN (...) for set membership tests ¨ Example: 🞑 Find customers with both an account and a…
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