user: Question: How many coins have a diameter of 23mm?
Columns: ['Value', 'Diameter', 'Thickness', 'Mass', 'Composition', 'Edge', 'Obverse', 'Reverse', 'first minting', 'issue', 'withdrawal', 'lapse']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'real', 'text', 'text', 'text']
Sample row: ['10 h', '15.5mm', '1.7mm', '0.6 g', '99% aluminium 1% magnesium', 'Plain', '"ČESKÁ REPUBLIKA", Czech lion , year of minting', 'Value, stylized river', 1993.0, '12 May 1993', '31 October 2003', '31 October 2009']
SQL:

assistant: SELECT COUNT("Reverse") FROM "Table" WHERE "Diameter" = '23mm';