user: Question: Who was the incumbent when ran William B. Oliver (D) Unopposed?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Alabama 1', 'Oscar Lee Gray', 'Democratic', 1914.0, 'Retired Democratic hold', 'John McDuffie (D) Unopposed']
SQL:

assistant: SELECT "Incumbent" FROM "Table" WHERE "Candidates" = 'William B. Oliver (D) Unopposed';