1. select sleep(2);執行睡眠2秒

2.

delete from tablename：清空一個表內容，但不清空表結構，該表格仍然存在，而且表格中列的資訊不會改變

drop table tablename：不但刪除表內容，而且使用droptable命令則會將整個資料庫表格的所有資訊全部刪除。

truncate tablename :刪除資料行，但保留表結構

3.

刪庫：

drop database if exists bfb_db_finance_20200831;

刪表：

drop table if existsbfb_db_cas_20200811.t_receive

drop table if existsbfb_db_cas_20200811

drop table if existsbfb_db_cas_20200811.t_transact_refund_log

DB_CONNECTOR="-h 10.10.10.10 -P 3306 -u user -p123123" 
DB_CMD="mysql $DB_CONNECTOR"
#刪除此時間之前的資料庫或表
begintime="20200901"
n=0;
while true; do
#日期後退
now=`date  +"%Y%m%d" -d  "+${n} days"`

if [ ${now} -lt $begintime ]; then

$DB_CMD -e "drop database if exists bfb_db_finance_${now}" >> log.log 
echo "bfb_db_finance_${now} has been deleted" >>log.log
sleep 3

$DB_CMD -e "drop table if exists bfb_db_cas_${now}.t_transact_refund_log"
echo "bfb_db_cas_${now}.t_transact_refund_log has been deleted" >> log.log
sleep 3

$DB_CMD -e "drop table if exists bfb_db_cas_${now}.t_receive"
echo "bfb_db_cas_${now}.t_receive has been deleted" >> log.log
sleep 3

$DB_CMD -e "drop table if exists bfb_db_cas_${now}.t_transact"
echo "bfb_db_cas_${now}.t_transact has been deleted" >> log.log
sleep 3

fi
let n-- 
sleep 0.1 
                                                                                                                                
done