SQL itself is case insensitive. By convention SQL statements are
always capitalized. I often type them in with lower case. But I
commit them to code capitalized.
There are many conventions developed over the years. I have worked
with several legacy systems with all manor of different styles. I
like the one where tables are plural, and the db id is simply "id".
Keeping a regular convention uniformly across a database makes it
easier to use. Can just type in queries without needing to look every
detail up all of the time.
The language has been around for 40 years and so there are many, many,
many operations built into SQL.
These are all simple examples just to show you the deep basics.