date_trunc_ym
Truncates a calendar date at the year/month threshold
Examples:
date_trunc_ym(to_fixed_timestamp('2017-12-13T00:24:53Z'))
-- Result: "2017-12-01T00:00:00Z"
date_trunc_ym(to_floating_timestamp('2017-12-13T00:24:53Z'))
-- Result: "2017-12-01T00:00:00"
date_trunc_ym(to_fixed_timestamp('2017-11-30T23:24:53-0930'))
-- Result: "2017-12-01T00:00:00Z"
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