CS 3430 Lecture Notes - Lecture 20: Carbon-13 Nuclear Magnetic Resonance, Boolean Function, Tuple
19 Apr 2018
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More sql: complex queries, triggers, views, and schema modification. Specifying semantic constraints as assertions and actions as triggers: more complex sql retrieval queries, views (virtual tables) in sql. Not applicable: null is not a data value! We cannot use equal operator = to check null attributes! Sql allows queries that check whether an attribute value is null by is null or is not null: query 18. Retrieve the names of all employees who do not have supervisors. Using select-from-where statement within where clause of another query. To understand nested queries, consider them as two for-loops inside each other; For each tuple in outer query, run the inner query and see if there is any result. To write queries you may need to look at the schema diagram of company database: In which table are first name and last name: how could you know if an employee is a department manager, now compile everything as a nested query:
