user: Question: What is the number of goals when the position is df, the nationality is england, and the Crewe Alexandra career is 1948–1951?
Columns: ['Name', 'Nationality', 'Position', 'Crewe Alexandra career', 'Appearances', 'Goals']
Types: ['text', 'text', 'text', 'text', 'real', 'real']
Sample row: ['Herbert Swindells Category:Articles with hCards', 'England', 'FW', '1927–1937', 280.0, 137.0]
SQL:

assistant: SELECT "Goals" FROM "Table" WHERE "Position" = 'df' AND "Nationality" = 'england' AND "Crewe Alexandra career" = '1948–1951';