[GENERAL] correlated query as a column and where clause

[salah jubeh]

Hello All,

I am wondering,  why I can not add the following  '  A > 10'  in the where  
clause  i.e.   'where nspname !~* 'pg_'  and A > 10'

Select nspname, (SELECT count(*) as count FROM pg_tables where schemaname = 
nspname) as A 

FROM pg_namespace
where nspname !~* 'pg_' 


Thanks in advance