追加 or null 的原因找到了:
https://stackoverflow.com/questions/5011239/why-do-i-need-or-null-in-mysql-when-counting-rows-with-a-condition
https://stackoverflow.com/questions/5011239/why-do-i-need-or-null-in-mysql-when-counting-rows-with-a-condition
2017-08-19
同學們把注意力應該切換到講師內容本身,畢竟免費的知識,其實老師也只是講了個大概,比如分區那塊,有分表,分庫,冷熱數據分離,很多知識沒有講述
2017-07-30