user: Question: What is the total number of Post, when Trainer is "steve asmussen", and when Time/ Behind is 19 ½?
Columns: ['Finished', 'Time/ Behind', 'Post', 'Horse', 'Jockey', 'Trainer', 'Owner']
Types: ['real', 'text', 'real', 'text', 'text', 'text', 'text']
Sample row: [15.0, '31 ¾', 1.0, 'Cool Coal Man', 'Julien Leparoux', 'Nick Zito', 'Robert V. LaPenta']
SQL:

assistant: SELECT SUM("Post") FROM "Table" WHERE "Trainer" = 'steve asmussen' AND "Time/ Behind" = '19 ½';