Is it recommended to make such a selection from the database?

Question

MySQL

SELECT * FROM table WHERE ID = (SELECT ID FROM second_table WHERE Name="Test")

Or is it better to write the ID once into a variable (on the server), and then choose from it?
And a related question. Is it possible to write the value NOW() to a text cell?

Answer 1

1. maybe you meant it?
And if at you selection changes under nested request? Will you have to hardcode the value into a variable again?
You can’t do this, you can cache the result, that’s another story.
2. It is possible to write down NOW () in text. but why only?

Answer 2

SELECT * FROM table WHERE ID = (SELECT ID FROM second_table WHERE Name="Test")

See for yourself, the more data you have in the desired table, the longer the query will be executed. It is not good when a subquery is executed with each WHERE iteration. In your case JOIN would be the best solution

Answer 3

There is no single answer to your question. Depends on the size of the database, the presence of indexes, and how often you run such a query.
If the request is made frequently, save the ID and then use it.