Is it possible to select all the rows(from all the pages) in a paging grid using SAIL?

Yes it can be possible, but you have to build that feature by your own as Appian don't provide that functionality

you can create a dynamic link on click of which all rows will be selected
once you click on that link it should save all the unique identifiers of the cdt data that you are displaying (primary key generally)
create one expression rule and query only the unique identifier for that CDT, from this rule you will receive a list of all the unique identifiers of the cdt structure that you have created(don't forgot to parse all the identifiers using tointerger() function {generally all the primary keys will be autogenerate numbers only})

So, when you click that link
a!save(
local!selected,
rule!nameofexpressionrule()
)

Here local!selected is the variable that is keeping values of the rows which are selected or not

Hope this will work for you.

Yes it can be possible, but you have to build that feature by your own as Appian don't provide that functionality

you can create a dynamic link on click of which all rows will be selected
once you click on that link it should save all the unique identifiers of the cdt data that you are displaying (primary key generally)
create one expression rule and query only the unique identifier for that CDT, from this rule you will receive a list of all the unique identifiers of the cdt structure that you have created(don't forgot to parse all the identifiers using tointerger() function {generally all the primary keys will be autogenerate numbers only})

So, when you click that link
a!save(
local!selected,
rule!nameofexpressionrule()
)

Here local!selected is the variable that is keeping values of the rows which are selected or not

Hope this will work for you.