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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '75a66329f9689916e87e9999caf40982d16e31d9687ebc088f1310879e19a352' 
  AND token = 'BHqkHnNUePsOSCUwN3wbNhtR1RFLMjSMJJaehGp5vj4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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