Could you explain a bit more about the integer datatypes and space (unsigned vs signed)?


In the integer datatypes and space section, there's a mediumint(9) example which purposefully ignores the 9. I'm curious, what does the 9 mean? Is it the same as char(9), like up to 9 digit numbers allowed?

How is varchar able to change the amount of storage it allocates? Is it something like Pointers?


When using enum, is this case sensitive? Will it matter whether we input ""CAT"" or ""cat"" when we insert values?

Given that ENUM is mutually exclusive, how would we approach a situation where let's say an animal can be of two types (like a liger, it's both tiger and lion). In other words, do you still recommend using enum and call it a liger, or for things that can belong to multiple different categories, would we use SET? 

I am a bit confused about why in the Key constraint part of the reading, the table with the key fails to add the content. I understand that keys are important when we are searching for values across tables, but I dont understand the essentials of why not having a primary key causes this error. Could we go over this in class? 


When using mysql dump, you say that it will allow us to restore the database to an earlier point in time. How far back in time would it allow us to go back? Are we only able to restore the latest database, or could we restore one from days/weeks/months ago? 

In the example where you insert values on the pets characteristics, you wrote ""insert into pet1 values ... etc "" is this line both creating and initializing pet1, or would we need to do it separately before writing this line?"


Can we please go over AUTO_INCREMENT? I did not understand how this would work practically. 

When using auto_increment, do you have to specify it when creating the table, or does every table have it automatically?

Is there a function equivalent to auto_increment that would have a different format or would allow the format to be adjusted by the user like including letters in the beginning or within the id? For example, with Cnumbers they might as well be just an incremented number with 1 letter in front of them, so it seems redundant to have 2 columns per student: 1 with Cid and 1 with auto_increment id. However, when creating new entries for new students you wouldn't want to have people manually have to check the last id in the table to come up with the next Cid.Or like license plates that have to be unique but have both letters and numbers?

What is a good way to verify what we are deleting is actually what we want to delete? Is there like a similar ls command for SQL in this way?