graph/db+sqldb: impl PruneGraphNodes

Which lets us run `TestChannelEdgePruningUpdateIndexDeletion` against
our SQL backends.

sqldb/sqlc/graph.sql.go

@@ -149,6 +149,16 @@ func (q *Queries) DeleteExtraNodeType(ctx context.Context, arg DeleteExtraNodeTy
 	return err
 }
 
+const deleteNode = `-- name: DeleteNode :exec
+DELETE FROM nodes
+WHERE id = $1
+`
+
+func (q *Queries) DeleteNode(ctx context.Context, id int64) error {
+	_, err := q.db.ExecContext(ctx, deleteNode, id)
+	return err
+}
+
 const deleteNodeAddresses = `-- name: DeleteNodeAddresses :exec
 DELETE FROM node_addresses
 WHERE node_id = $1
@@ -1219,6 +1229,51 @@ func (q *Queries) GetSourceNodesByVersion(ctx context.Context, version int16) ([
 	return items, nil
 }
 
+const getUnconnectedNodes = `-- name: GetUnconnectedNodes :many
+SELECT n.id, n.pub_key
+FROM nodes n
+WHERE NOT EXISTS (
+    SELECT 1
+    FROM channels c
+    WHERE c.node_id_1 = n.id OR c.node_id_2 = n.id
+)
+AND NOT EXISTS (
+    SELECT 1
+    FROM source_nodes sn
+    WHERE sn.node_id = n.id
+)
+`
+
+type GetUnconnectedNodesRow struct {
+	ID     int64
+	PubKey []byte
+}
+
+// Select all nodes that do not have any channels.
+// Ignore any of our source nodes.
+func (q *Queries) GetUnconnectedNodes(ctx context.Context) ([]GetUnconnectedNodesRow, error) {
+	rows, err := q.db.QueryContext(ctx, getUnconnectedNodes)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []GetUnconnectedNodesRow
+	for rows.Next() {
+		var i GetUnconnectedNodesRow
+		if err := rows.Scan(&i.ID, &i.PubKey); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Close(); err != nil {
+		return nil, err
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const getV1DisabledSCIDs = `-- name: GetV1DisabledSCIDs :many
 SELECT c.scid
 FROM channels c