Can a subquery be used in an Oracle ALTER statement?

Question

Given a table name and a column name, I'm trying to dynamically drop an Oracle constraint that I don't know the name of ahead of time.

I can find the constraint name with this query:

SELECT CONSTRAINT_NAME 
 FROM USER_CONS_COLUMNS 
 WHERE TABLE_NAME = 'MyTable' AND 
 COLUMN_NAME='MyColumn' AND POSITION IS NULL

My first thought was to use a subquery, but that doesn't work and results in an ORA-02250 error:

ALTER TABLE MyTable 
  DROP CONSTRAINT (
   SELECT CONSTRAINT_NAME 
    FROM USER_CONS_COLUMNS 
    WHERE TABLE_NAME = 'MyTable' AND 
    COLUMN_NAME='MyColumn' AND POSITION IS NULL)

So far, the only working solution I have is the following, but it feels unnecessarily complex:

DECLARE 
statement VARCHAR2(2000);
constr_name VARCHAR2(30);
BEGIN
  SELECT CONSTRAINT_NAME INTO constr_name 
   FROM USER_CONS_COLUMNS 
   WHERE table_name  = 'MyTable' AND 
   column_name = 'MyColumn' AND position is null;
   statement := 'ALTER TABLE MyTable DROP CONSTRAINT '|| constr_name;
   EXECUTE IMMEDIATE(statement); 
END;
/

Is there a way to do this with a subquery, as I originally intended? If not, can anyone suggest a more concise way to do this?

Answer 1

You cannot. SQL and DDL are basically two separated languages. Your solution is correct.