instruction: what was the first time that patient 57023 got a microbiology test during a month before?
response: SELECT microbiologyevents.charttime FROM microbiologyevents WHERE microbiologyevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 57023) AND DATETIME(microbiologyevents.charttime, 'start of month') = DATETIME(CURRENT_TIME(), 'start of month', '-1 month') ORDER BY microbiologyevents.charttime LIMIT 1