MySQL Point

1.索引

2. group by where having order by
   https://blog.csdn.net/whathellll/article/details/80765020

3. concat
   https://baijiahao.baidu.com/s?id=1595349117525189591&wfr=spider&for=pc

4. 俩练习
   https://blog.csdn.net/feinifi/article/details/80279897

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6.round
https://www.runoob.com/sql/sql-func-round.html
https://blog.csdn.net/chinabestchina/article/details/72799826

7.count

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8.distinct

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9.group by

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10.having

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11.执行顺序

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12.子查询

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13.自连接,一个题

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14.表和视图
https://blog.csdn.net/m0_37248802/article/details/80563691