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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b4e51b04c5128d726f9977644e89699f321abd3d48e7523274496a21a94651aa' 
  AND token = 'C1z30QoPraAtFPIWw/aIAlOwrvfb096HYDhkobGEACM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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