MySQL sort null value

Starting from the realistic project demand;
There is a city table;
There are Beijing, Shanghai, Guangzhou, Hebei, Tianjin, Henan 6 cities;

Mysql>Select*From Bjy_order;+----+------+| Id| City|+----+------+| 1 | Beijing || 2 | Shanghai || 3 | Guangzhou || 4 | Hebei || 5 | Tianjin || 6 | Henan |+----+------+           

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The requirement is to let Shanghai row the first, Tianjin row second;
The simplest and most brutal method is to add a order_number field;
Used to identify the order;
Then by order by order_number asc  sorting

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Mysql>Select*From Bjy_orderOrderby Order_numberAsc;+----+------+--------------+| Id| City| Order_number|+----+------+--------------+|2| Shanghai|1||5| Tianjin|2|| Beijing | 1 | 3 || 3 guangzhou |  4 || Hebei, 4 |  5 || 6- Henan | 6 |  +----+------+--------------+ 

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Doing so does satisfy demand;
But what if the table contains all 32 provinces in China?
If you come to a national county and city table hundreds of data?
And we just want to get some values in front of the line;
Just as most people only know that the first peak of the world is Mt. Everest without paying attention to the second third;
The first thing we should think about is to just give the sort numbers that need to be in front, and the other is null;

Mysql>Select*From Bjy_order;+----+------+--------------+| Id| City| Order_number|+----+------+--------------+|1| Beijing|Null||2| Shanghai|1||3 guangzhou |  NULL || Hebei, 4 |  NULL ||  Tianjin | 5 | 2 || 6- Henan | NULL |  +----+------+--------------+ 

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Then we order by a bit;

Mysql>Select*From Bjy_orderOrderby Order_numberAsc;+----+------+--------------+| Id| City| Order_number|+----+------+--------------+|1| Beijing|Null||3| Guangzhou|Null||Hebei, 4 |  NULL || 6- Henan | NULL ||  Shanghai | 2 | 1 ||  Tianjin | 5 | 2 |  +----+------+--------------+ 

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But what is frustrating when it is about to succeed;
Those are the null rows at the front;
OK, here is the main character of today to solve this problem;
Let's use is null the SQL for a little makeover.

Mysql>Select*From Bjy_orderOrderby Order_numberIsNull, Order_numberAsc;+----+------+--------------+| Id| City| Order_number|+----+------+--------------+|2| Shanghai|1||5| Tianjin|2||1 | Beijing | null || 3 | Guangzhou | null || 4 | Hebei | null || 6 | Henan | null | +----+------+--------------+          

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To achieve the perfect demand;

MySQL sort null value