user: Question: What was the date that construction was finished when the unit was Greifswald - 4 (KGR 4)?
Columns: ['Unit', 'Type', 'Net Power', 'Total Power', 'Finish construction']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Greifswald - 1 (KGR 1)', 'WWER-440/230', '408 MW', '440 MW', '17.12.1973']
SQL:

assistant: SELECT "Finish construction" FROM "Table" WHERE "Unit" = 'Greifswald - 4 (KGR 4)';