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Building Database Applications in PHP Week 2 Practice Quiz Answer

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PDO

Question 1) Why is it important to have extensive error checking on SQL statements when an application is in production?

• Tracebacks make your application look bad
• The developer/production team needs good detail on any errors
• Users will rarely report errors and never give enough detail
• Some errors are subtle and only show up very rarely
• All of the above

Question 2)What is the purpose of the PDO::errorinfo() data?

• It combines the prepare() and execute() phases of PDO into a single call
• It allows you to choose the style of error handling for your application
• It allows you to register a callback function to be called in case of an unhandled error
• It gives extended detail when a PDO function returns an error

Question 3) How is a LEFT JOIN different from a regular JOIN?

• In a LEFT JOIN rows can come from either the left table or right table as long as the row matches the WHERE clause
• All of the text fields are left aligned in the result set
• In a LEFT JOIN rows are included form the left table even if there is no matching row in the right table
• You do not need an ON clause for the LEFT JOIN

Question 4) What is a common use of GROUP BY in SQL?

• When combined with the COUNT function, it provides a way to compute sub-totals
• It is a faster way to sort fields than ORDER BY
• It is a way to choose which rows from a JOINed table are to be included in a result set
• It allows a result set to be broken into 20 row chunks for efficiency

Question 5) Why do subqueries have the potential to cause a query to execute slowly?

• Because subqueries don’t make use of indexes
• Because subqueries cannot use integer foreign keys
• Because subqueries must include all of the fields that are selected by the main query
• Because MySQL executes the subquery independently from the main query