Have a project for school and we are beginners in SAS programming.  We are having a bit of trouble merging an environmental dataset (daily data for 10 years) with a birth cohort dataset (n = ~350,000). Essentially, we want to tell SAS to start in the birth dataset (in which we have a subject ID, county of residence and  pregnancy date range for each individual subject (FirstDayPreg LastDayPreg), then go to the air quality data set and count the number of exceedances (ExpLevel coded as 0 or 1.  1 if exceeds daily threshold for various air quality metrics) within that pregnancy date range, and then output the number of exceedances by subject ID. We have tried to accomplish this with PROC SQL and nested DO loops, but can't quite seem to figure it out. An image of environmental data set and birth cohort data are attached.  We would really appreciate any assistance you can provide us.   Birth cohort data Environmental data ... View more