Exec a text variable as select

[Ranieri Mazili <ranieri.oliveira@xxxxxxxxxxxx>]

Hello,

I'm creating a function that will create a select statement into a 
while, this select will be stored into a text variable, after while ends 
I need to execute this query stored into variable, on SQLSERVER I can do:
EXEC(text_variable)
How can I do this on Postgres?

I appreciate any help
Thanks