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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50a66f7d81bbd41126cced94e1c5fa0a5376f4c02050e7551a2d66c25a62b615' 
  AND token = '5KGd/PJRAoJfBTsqRdL+Jeo1anhtSYFvVXQlIiyT7Lc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00032

JSON explain

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