How do I check a column in a table in a SQL query

You should do something like this:

= Sql.Database("Northwest", "Reporting", [Query="SELECT DISTINCT SUBSTRING([IssueKey],1,(CHARINDEX('-', [IssueKey])-1) ) AS TeamProject#(lf)FROM [Reporting].[dbo].[SprintIssuesSummaryEOS] WHERE Sprint IN#(lf)(SELECT Sprint#(lf)FROM dbo.SprintDates#(lf)WHERE SprintStartDate = " & CurrentSprintInfo[PriorSprintDate] & " and SprintEndDate = " & CurrentSprintInfo[PriorSprintEndDate] & ")"

So, idea is to have a concatenated string here, where you will pass your values. Instead of "." notation you use square brackets to provide the column names. But now the question is what are the values that you want to pass there? Are these a single values only, or you want to apply it for the entire table, row by row? If the second option is valid here, you should ditch the table name, and reference columns only. If the first option is your scenario, then you must additionally drill down to single value within column structure like this: CurrentSprintInfo[PriorSprintDate]{0}.