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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b8f8d1805c36d8f6be5f32624f82fda8cbdfa1448a0eaaedc14dee7e84967ab6' 
  AND token = 'KTbDu1pQqZMZ0NtHXAJCZws4UNuRg6rGn9MC+Jx+CNw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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