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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '68b2bec0016980903ba847874b2a3317dd6a2d85884f4c12cb0eaa50fbd0f571' 
  AND token = '8Q1UAdhoAZQQqIeIXuSZm+I+FWxDDs8PX5oYKBMsTQE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00042

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}