user: Question: What's the diameter of the 2006 Equestrian Reverse?
Columns: ['Year', 'Denomination', 'Reverse', 'Weight', 'Diameter', 'Fineness', 'Series']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [2006.0, '150 Yuan', 'Equestrian', '.33 Troy Ounce', '23mm', '.9999 Gold', 'I series']
SQL:

assistant: SELECT "Diameter" FROM "Table" WHERE "Year" = 2006.0 AND "Reverse" = 'Equestrian';