user: Question: How many values of r z(arcsecond) are associated with a target datum of Ireland 1965?
Columns: ['Region', 'Start datum', 'Target datum', 'c_x ( Metre )', 'c_y (Metre)', 'c_z (Metre)', 's ( ppm )', 'r x ( Arcsecond )', 'r y ( Arcsecond )', 'r z ( Arcsecond )']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Slovenia ETRS89', 'D48', 'D96', '409.545', '72.164', '486.872', '17.919665', '−3.085957', '−5.469110', '11.020289']
SQL:

assistant: SELECT COUNT("r z ( Arcsecond )") FROM "Table" WHERE "Target datum" = 'Ireland 1965';