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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c0187f3e2eb6662fc5318d398d05ebd1939ede347b2df08d29015dce8a708c19' 
  AND token = 'zMDa2oAgQVfr2+Zgf2ep25qQVoNPWOEJ2a+CTXeaVRM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

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