我不知道该函数是为每一行计算一次还是更多.这取决于查询优化器.你可以通过基准来建立它.

I cannot tell if the function is evaluated once for each row or more. It depends on the query optimizer. You could establish it by benchmark.

无论如何，这个查询是非常低效的.它将执行全表扫描并为每一行计算此函数.您不能在此处使用索引.您不会在具有多于几行的表上实现此查询.

Anyway, this query is very inefficient. It will do a full table scan and calculate this function for each row. You cannot use an index here. You would not implement this query on a table with more than a couple of rows.