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What does this query mean: SELECT user_name, user_isp FROM users LEFT JOIN isps USING (user_id)

It’s equivalent to saying SELECT user_name, user_isp FROM users LEFT JOIN isps WHERE users.user_id=isps.user_id

How do you find out which auto increment was assigned on the last insert?

SELECT LAST_INSERT_ID() will return the last value assigned by the auto_increment function. Note that you don’t have to specify the table name.

What does –i-am-a-dummy flag to do when starting MySQL?

Makes the MySQL engine refuse UPDATE and DELETE commands where the WHERE clause is not present.

On executing the DELETE statement I keep getting the error about foreign key constraint failing. What do I do?

What it means is that so of the data that you’re trying to delete is still alive in another table. Like if you have a table for universities and a table for students, which contains the ID of the university they go to, running a delete on a university table will fail if the students table still contains people enrolled at that university. Proper way to do it would be to delete the offending data first, and then delete the university in question. Quick way would involve running SET foreign_key_checks=0 before the DELETE command, and setting the parameter back to 1 after the DELETE is done. If your foreign key was formulated with ON DELETE CASCADE, the data in dependent tables will be removed automatically.

When would you use ORDER BY in DELETE statement?

When you’re not deleting by row ID. Such as in DELETE FROM techinterviews_com_questions ORDER BY timestamp LIMIT 1. This will delete the most recently posted question in the table techinterviews_com_questions.

How can you see all indexes defined for a table?

SHOW INDEX FROM techinterviews_questions;

How would you change a column from VARCHAR(10) to VARCHAR(50)?

ALTER TABLE techinterviews_questions CHANGE techinterviews_content techinterviews_CONTENT VARCHAR(50).

How would you delete a column?

ALTER TABLE techinterviews_answers DROP answer_user_id.

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