mysql MIN（）集計関数で科学的記数法と10進数を比較するにはどうすればよいですか？

10進数にキャストすると役立つはずです：-

mysql> select cast( "5.89872212195226e-05"  as decimal(65,30));
+--------------------------------------------------+
| cast( "5.89872212195226e-05"  as decimal(65,30)) |
+--------------------------------------------------+
|                 0.000058987221219522600000000000 |
+--------------------------------------------------+

比較例：-

mysql> select least( 4, cast("5.89872212195226e-05" as decimal(65,30)) );
+------------------------------------------------------------+
| least( 4, cast("5.89872212195226e-05" as decimal(65,30)) ) |
+------------------------------------------------------------+
|                           0.000058987221219522600000000000 |
+------------------------------------------------------------+

使用例：-

MIN(cast( ...  as decimal(65,30)))