You have a table books with columns author and title. How would you write a query to list each author with all their book titles concatenated, separated by commas?

hard📝 Application Q8 of 15

PostgreSQL - Aggregate Functions and GROUP BY

You have a table books with columns author and title. How would you write a query to list each author with all their book titles concatenated, separated by commas?

ASELECT author, STRING_AGG(title) FROM books;

BSELECT author, STRING_AGG(author, ', ') FROM books GROUP BY title;

CSELECT author, STRING_AGG(title, ';') FROM books;

DSELECT author, STRING_AGG(title, ', ') FROM books GROUP BY author;

Step-by-Step Solution

Solution:

Step 1: Group by author to aggregate titles per author
We need to group rows by author to combine their titles.
Step 2: Use STRING_AGG on title with comma separator
STRING_AGG(title, ', ') concatenates titles with commas.
Final Answer:
SELECT author, STRING_AGG(title, ', ') FROM books GROUP BY author; -> Option D
Quick Check:
Group by author + STRING_AGG titles with comma [OK]

Quick Trick: Group by author, aggregate titles with STRING_AGG [OK]

Common Mistakes:

Omitting GROUP BY author
Missing separator argument
Aggregating wrong column

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You have a table books with columns author and title. How would you write a query to list each author with all their book titles concatenated, separated by commas?

Step 1: Group by author to aggregate titles per author

Step 2: Use STRING_AGG on title with comma separator

Final Answer:

Quick Check:

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