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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51823e6c7b69fc0bfe4eb656a00bbbe18601cbe4994f8210fedaf3056cfd0774' 
  AND token = 'RfpS3p8nJ4EiHVYusJj8lh+h2fKc1+DyF6obK8gxRCU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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