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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'c375e2d969383b0c061ea8b2eb799d1be78d03dfe171e11a80e21e6058774d67' 
  AND token = 'Manch+KBknDgXVWhkv8cdS5IA32pwI0MDsvyOyFxOzU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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