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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b51c617b4e5531bd0d35e787c6a1ab6288fdeb9506f542e0a6f38bd0a7a93288' 
  AND token = '44+QgLve6LUAI+4w2rS62FYEFbrQ3qVLEBrUDM2fx4I=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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