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What does the EXISTS operator return if the subquery returns any rows?

Error

True

100%

Null

False

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Match the SQL subquery operator with its function

Checks if a subquery returns any rows

Keyword is commonly used to introduce a subquery

Compares a value with the result of a subquery that returns multiple rows

Checks if a subquery returns no rows

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Which type of subquery is evaluated for each row processed by the outer query?

Non-correlated subquery

Scalar subquery

Nested subquery

Correlated subquery

Which operator is used ...

(match the appropriate)

to compare for equality a single value with the result of a subquery?

to check if a subquery returns no rows?

to compare by more/less a value with the result of a subquery that returns a single column and a single row?

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Which type of subquery is executed once for the entire outer query?

Scalar subquery

❌

Non-correlated subquery

Correlated subquery

Nested subquery

Assuming that we have 2 tables - customers and orders:

Assuming the following query

select * from customers join orders on orders.customer_id = customers.customer_id;

It will not bring the customers that they have never put an order.

True

False

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Which of the following is not true about NATURAL JOINs?

Natural joins are not based on primary/foreign keys

❌

Natural join is based on all columns in two tables having same name

❌

It selects rows from the two tables having different values in the matched columns

✅

If columns having same names have different data types, it returns error

❌

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Which of the following is NOT a commonly accepted rule for joining multiple tables?

It is recommended that aliases be keywords to keep the statement uniform throughout the query

✅

It is recommended that joins between tables are based on Primary/Foreign keys

❌

Put join conditions before other conditions in the WHERE clause when using implicit join

❌

Any table listed in a join condition MUST exist in the FROM clause when using implicit join

❌

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A UNION query is which of the following?

Combines the output from multiple queries and does not include the same number of columns

❌

Combines the output from multiple queries and must include the same number of columns

✅

Combines the output from no more than two queries and must include the same number of columns

❌

Combines the output from no more than two queries and does not include the same number of columns

❌

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What type of join is needed when you wish to include rows that do not have matching values?

INNER JOIN

SELF JOIN

OUTER JOIN

CROSS JOIN

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