SAS PROC SQL验证

Question

I wonder may I ask a question in terms of "PROC SQL VALIDATE" as follows:

Which statement about the following PROC SQL query is "false"?

    proc sql;
validate
select name label="Country",
rate label="Literacy Rate"
from world.literacy 
where "Asia" =
(select continent 
from world.continents
where literacy.name=
continents.country)
order by 2;

I wonder why the first options below is not "false"?

 (a) The query syntax is not valid. 

 (b) The outer query must pass values to the subquery 
    before the subquery can return values to the outer 
    query

(c) PROC SQL will not execute this query when it is
    submitted   

(d) After the query is submitted, the SAS log will 
    indicate whether the query has valid syntax

The answer is (d) I was wondering why the query syntax is not valid?

Thank you very much!!

Answer 1

The query that you have posted has a correlated sub-query ( from world.continents ). This sub-query cannot be evaluated independently, but actually depends on the values passed to them by the outer query ( world.literacy ).

Let me explain each of the 4 options,

(a) The query syntax is not valid. - False

No, this is totally valid statement, where we have an outer-query and a sub-query.

(b) The outer query must pass values to the subquery before the 
    subquery can return values to the outer query - True

As mentioned on the top, this is what actually happens.

(c) PROC SQL will not execute this query when it is submitted - True

As you can see in the doumentation , a validate statement only checks for the accuracy of a query expression's syntax and semantics without executing the expression.

(d) After the query is submitted, the SAS log will 
    indicate whether the query has valid syntax - True

The same documentation also mentions that validate statement writes a message in the SAS log that states that the query is valid. If there are errors, then validate writes error messages to the SAS log.