MYSQL - Unknown column 'a' in 'field list' -

when running query works perfectly:

select 10 a;

but when using column a

select 10 a, (a - 1) b

i following error: unknown column 'a' in 'field list'

why isn't working way?

you can't reuse alias in same select statement in defined. perhaps closest thing want here this:

select     t.a,     (t.a - 1) b (select 10 dual) t;

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