Check out the solution in the video TSQL: Find Values In One Table Not In Another Table. In the example, we see how to identify data in one table that does not exist in another table. This may be extremely useful in downstream data where we find missing data (by counts).
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In most cases, missing data may not make through filters. This could either be good or bad, depending on what we'd expect. In the best case scenario, this is expected. In the worst case scenario, we may find that our data source has provided us with poor data.