MySQL函数find_in_set优化使用

1、find_in_set()问题

find_in_set会使用全表扫描，导致查询效率很低

2、改进之前的语句

select * from `persons` where `logout` = '0' and FIND_IN_SET(unitcode, getChildList('%', 1));
---query time
---2.5s
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3、改进之后的语句

select * from `persons` inner join (select getChildList('%', 1) unitlist) x on `unitlist`=`unitlist` and  FIND_IN_SET(unitcode, unitlist)  where `logout` = '0';
---query time
---0.06s
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4、Laravel中的使用

    public function scopeAtunit($query, $unitcode)
    {
        $unitcode = $unitcode ? $unitcode : '%';
        return $query->join(DB::raw("(select getChildList('{$unitcode}', 1) unitlist) x"), function ($join) {
            $join->on('unitlist', '=', 'unitlist')
                ->whereRaw('FIND_IN_SET(unitcode, unitlist)');
        });

        //return $query->whereRaw('FIND_IN_SET(unitcode, getChildList(?, 1))', [$unitcode]);
    }
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