Changing a MySQL setting failed with ERROR 1227 (42000): Access denied; you need (at least one of) the SUPER or SYSTEM_VARIABLES_ADMIN privilege(s) for this operation. The word GLOBAL in the statement is the cause. Most of the time you don't want the whole server changed anyway, and one word fixes it.
I wanted to see which transactions were open, and MySQL said ERROR 1227 (42000): Access denied; you need (at least one of) the PROCESS privilege(s) for this operation. The account has full rights on its own database, and that's not enough. Here's why, and the right way to fix it without making your application's account more powerful.
An UPDATE hung for a while, then failed with ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction. Raising the timeout is the tempting fix, and the wrong one, because the real problem is another transaction holding the row. Here's how to find it, and a surprise about what the error leaves behind.
An ordinary UPDATE failed with ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction, and MySQL threw away everything the transaction had done so far. Two transactions had taken the same rows in opposite orders. Here's how to see that for yourself, and the small change that stops it.
curl http://localhost:5190/demo/enum?status=placed and grep -rn 'class' src --include=*.cs both failed with zsh: no matches found, and neither program ever ran. Commands like these work in bash, and they appear that way in a lot of tutorials. In zsh, you have to quote them.
My script fed commands to a program through a named pipe. It closed the pipe when it was done, and waited for the program to finish, and that wait never ended. Another process had a copy of the pipe open, and I'd given it that copy without noticing.
I stopped my API with pkill -f, and a long script in another terminal died too, with exit code 143 and no error message. The script wasn't the API. It only had the API's name somewhere in its command line, and that's all -f needs.
xargs stopped partway through a list with xargs: command line cannot be assembled, too long. The command was only about 250 characters, and the system allows over a million. The limit that matters here is a much smaller one, and it applies only with -I.
Part 2 created the tables, and they're still empty. In this part the API starts using them: you'll insert, read, change and delete rows through real endpoints, and read the SQL that EF Core sends to MySQL for every one of them. You'll also turn MySQL's refusals, such as a duplicate name, into clear HTTP answers, and stop two people from silently overwriting each other's changes.
When an UPDATE sets a column to the value it already has, did it affect the row? MySQL can answer either way, and a connection string option decides which you get. With Oracle's connector, the default is "yes", and that matters more than it looks. Turn the option on, and EF Core starts throwing an exception on some ordinary saves.
