mysql函数返回表的第一个'X'百分位结果

Question

我想创建一个mysql函数，它返回表的第一个“X”百分位数。我尝试了下面给出的并且收到错误..

任何想法/建议请...

create function precent_return (
    table_name varchar(50),
    percentiles float
) returns int
return (count(*)*percentiles/100 from table_name)

Answer 1

您需要使用动态SQL：

create function precent_return (
    in_table_name varchar(50),
    in_percentiles float
) returns int
begin
    set @retval = -1;
    set @sql = 'select count(*) * @percentiles/100 into @retval from @table_name';
    set @sql = replace(@sql, '@percentiles', in_percentiles);
    set @sql = replace(@sql, '@table_name', in_table_name);

    prepare stmt from @sql;

    execute stmt;

    deallocate prepare stmt;

    return(@retval);
end;