user: Question: How many different PPI does the model with ppcm of 87 have?
Columns: ['Model', 'PPI (pixels per inch )', 'ppcm (pixels per cm )', 'Resolution', 'Typical viewing distance (in/cm)', 'Pixels per degree (PPD)']
Types: ['text', 'real', 'real', 'text', 'text', 'real']
Sample row: ['iPhone 4 / 4S and iPod Touch (4th generation)', 326.0, 128.0, '960×640', 'inches (cm)', 57.0]
SQL:

assistant: SELECT COUNT("PPI (pixels per inch )") FROM "Table" WHERE "ppcm (pixels per cm )" = 87.0;