CREATE TABLE table_19623 ("Explosion" TEXT, "Location" TEXT, "Date" TEXT, "Yield  ( approximate ) " TEXT, "Altitude  ( km ) " TEXT, "Nation of Origin" TEXT)

What was the yield of the K-4 explosion?
SELECT "Yield (approximate)" FROM table_19623 WHERE "Explosion" = 'K-4'
SELECT "Yield (approximate)" FROM "table_19623" WHERE "Explosion" = 'K-4'