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Category Archives: SQL
NULL values in SQL ¨ Additional SQL join operations 🞑 Natural join 🞑 Outer joins ¨ SQL views
¨ Values in UPDATE can be arithmetic expressions 🞑 Can refer to any attribute in table being updated ¨ Example: 🞑 Add 2%…
¨ SQL also has an UPDATE command for modifying existing tuples in a table 🞑General form: UPDATE table SET attel=vall, attr2=va12, . .…
SQL DELETE command can use a WHERE clause DELETE FROM table; 🞑 Deletes all rows in the table DELETE FROM table WHERE ...;…
¨ SQL provides many other options for inserting, updating, and deleting tuples All commands support SELECT-style syntax ¨ Can insert individual tuples into…
¨ Always take note when computing aggregates of aggregates! “Find the largest total account balance of any branch.” 🞑 Two nested aggregates: max…
¨ More typical is a query against aggregate values Example: “Find the largest total account balance of any branch.” 🞑 Need to compute…
¨ Subquery in FROM clause must be given a name 🞑 Many DBMSes also require attributes to be named SELECT customer_city, num_customers FROM…
“Find all cities with more than two customers living in the city.” SELECT customer_city, COUNT(*) AS num_customers FROM customer GROUP BY customer_city HAVING…
¨ Often need to compute a result in multiple steps Can query against a subquery’s results 🞑 Called a derived relation ¨ A…
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