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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '29dec515bda8da51963428c70328b17fb44f042fbd4909c508c0bb2f5268c0ac' 
  AND token = '/JfvfzoeoDyBgEuKfes1KbDRcC+JimTkkHhB49wzCls=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00032

JSON explain

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