have 1 ROW.  Dual is a normal table with one dummy column of varchar2(1).

This is basically used from several applications as a pseudo table for

getting results from a select statement that use functions like sysdate or other

prebuilt or application functions.  If DUAL has no rows at all some applications

(that use DUAL) may fail with NO_DATA_FOUND exception.  If DUAL has more than 1

row then applications (that use DUAL) may fail with TOO_MANY_ROWS exception.  

So DUAL should ALWAYS have 1 and only 1 row

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