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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '255f7fabdab21148b5451dd4638fdf2c0c2b94d0c5e170caecdbcfc899f5d2e8' 
  AND token = 'D8lelA5izTfEHWMIVQhiVdnKb5zgliI7jVUBnHbHI8Q=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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