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SELECT 
  1 
FROM 
  cscart_aprillock_keys 
WHERE 
  key_id = '421da43a9e6a036d6344582626b01f25d236976cf8907adebebea4bf4ce670cd' 
  AND token = 'EupCUYmPpDtDa+mhC/4jRXScZigAcCP8FddQDJP4goA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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