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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '688bdd43fef1dd37c0e4a41b45f4dee459c13b77e6671938a88e04ea7c979f00' 
  AND token = '3x+zikzmIydgYDml+Bpep7Urdj73s3uLjS3rSmbAiTc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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