在同一条sql语句中使用别名的值

Question

How can I use the value of an alias for display in the same sql statement?

For example:

select now() as t, concat('Hello: ', username, t) from table;

What I'm actually trying to do is a lot more complex. I've broken it down to this so you get the idea.

How can something like this be done so I neednt select the same column again?

Answer 1

You can not do that directly, but there's a way in MySQL to use variables like this:

select @t:=now() as t, concat('Hello: ', username, @t) from t;

If you don't need this t - you may want to remove that alias (I've kept just in case)

Answer 2

You can't re-use directly an alias in the select part of the same level of query.

You could use

a variable

select @myVar := now(), concat('Hello:', username, @myVar) from t;

a subquery

select concat('Hello:', username, t)
from (select now() as t, username from table1) s