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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c90a3c21f427fe7a482441c7eeb8c6e138cc01c26f9bbfc2a664d4d00ea592c1' 
  AND token = 'gC9dAj4ByH2RiMWkH+GDFF/51ZwOdlC1+yQLF8MONVM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00009

JSON explain

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