sqexplain.out 怎么分析

sqexplain.out 如何分析？

SQL code

  Table map :  ----------------------------  Internal name     Table name  ----------------------------  t1                psmsa  t2                cdssa  t3                psmsa_tmp  type     table  rows_prod  est_rows  rows_scan  time       est_cost  -------------------------------  scan     t1     46         4860      28897      00:00:31   22854     type     table  rows_prod  est_rows  rows_scan  time       est_cost  -------------------------------  scan     t2     46         281733    46         00:00:01   1         type     rows_prod  est_rows  time       est_cost  -------------------------------------------------  nljoin   46         4860      00:00:32   27264     type     rows_sort  est_rows  rows_cons  time  -------------------------------------------------  sort     46         4860      46         00:00:32  type     table  rows_ins   time  -----------------------------------  insert   t3     46         00:00:32