Where is the moving from location with a transfer window of summer and the source kerkida.net?
CREATE TABLE "squad_changes" (
  "nat" text,
  "name" text,
  "moving_from" text,
  "type" text,
  "transfer_window" text,
  "ends" real,
  "transfer_fee" text,
  "source" text
);
SELECT "moving_from" FROM "squad_changes" WHERE "transfer_window"='summer' AND "source"='kerkida.net';