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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b8b798bb201fd9e144eeed6e47a663966e7b799d3d0bfdb05ab18ce0d68ba48c' 
  AND token = 'q8iwBc7FM0SiJeXbPEd9gg+SbTZwxlUYHFLX8qkBN+Y=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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