What is the special operator used to check whether a subquery returns any rows?

     SELECT EMPNO, LASTNAME, SALARY
     FROM CORPDATA.EMPLOYEE
     WHERE EDLEVEL >
        (SELECT AVG(EDLEVEL)
           FROM CORPDATA.EMPLOYEE)

SQL first evaluates the subquery and then substitutes the result in the WHERE clause of the SELECT statement. In this example, the result is the company-wide average educational level. Besides returning a single row, a subquery can return no rows. If it does, the result of the compare is unknown.

... WHERE WORKDEPT NOT IN (SELECT …)

     SELECT EMPNO,LASTNAME
     FROM CORPDATA.EMPLOYEE
     WHERE EXISTS
        (SELECT *
           FROM CORPDATA.PROJECT
           WHERE PRSTDATE > '1982-01-01');

In the example, the search condition is true if any project represented in the CORPDATA.PROJECT table has an estimated start date that is later than January 1, 1982. This example does not show the full power of EXISTS, because the result is always the same for every row examined for the outer-level SELECT. As a consequence, either every row appears in the results, or none appear. In a more powerful example, the subquery itself would be correlated, and change from row to row.

As shown in the example, you do not need to specify column names in the select-list of the subquery of an EXISTS clause. Instead, you should code SELECT *.

You can also use the EXISTS keyword with the NOT keyword in order to select rows when the data or condition you specify does not exist. You can use the following:

A database language enables the user to perform complex queries designed to transform the raw data into useful information.

• A. 

  True

• B. 

  False

Below is a Relational Database Trivia Quiz! It is designed to help you understand how databases holding the same information are structured and maintained. Do you think that you have what it takes to tackle it based on what you...

Questions: 9  |  Attempts: 8715   |  Last updated: Mar 21, 2022

• Sample Question

  Which of the following makes it possible for entities toshare a relationship?
  

  Multi-valued attributes

  A foreign key

  A common attribute

  The same number of attributes

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Questions: 31  |  Attempts: 7781   |  Last updated: Mar 22, 2022

• Sample Question

  -------------------------------responsible for authorizing access to the database, for coordinating and monitoring its use, acquiring software, and hardware resources, controlling its use, andmonitoring efficiency of operations.

  What is the special operator used to check if an attribute is in a range?

  IST210Final.

  Which operator can you use to test whether one or more rows are returned by a subquery?

  The EXISTS Operator. The EXISTS operator check the number of rows returned by a subquery. If the subquery contains one or more rows, then the result is true and a row is placed in the result table; otherwise, the result is false and no row is added to the result table.

  Which operator is used to check whether an attribute value is null?

  The IS NULL operator is used to test for empty values (NULL values).

  What is an SQL operator to check whether an attribute value matches any value within the given list of values?

  The IN operator allows you to determine if a value matches any value in a list of values. Here's the syntax of the IN operator: value IN (value1, value2, value3,...) The IN operator returns 1 (true) if the value equals any value in the list ( value1 , value2 , value3 ,…).