我有一个select声明，结果是：
ax | country | country_id | town | pop |
1 | neverland | 1 | ntown | 10 |
1 | wonderland | 2 | wtown | 20 |
2 | wonderland | 2 | wLtown | 20 |
1 | toysIsland | 3 | ttown | 5 |
但它应该像这样：
ax | country | country_id | town | pop |
1 | neverland | 1 | ntown | 10 |
1 | wonderland | 2 | wtown | 20 |
2 | wonderland | 2 | wLtown | NULL|
1 | toysIsland | 3 | ttown | 5 |
我有一个if声明使用值来自case：
select (case country
when @c
then @co = @co +1
else @co = 1, @c = country
end ) as ax,
country, country_id, town, (case when town_id = param_ti then population_c) as pop
from tb_town a left join
tb_country b on b.country_id = a.country_id;
if ax = 1 then
pop= pop
else
pop= '';
end if;
我不知道该写些什么if。
尝试对您的查询进行此更改
select (case country when @c then @co = @co +1
else @co = 1, @c = country
end ) as ax,
country, country_id, town, IF(town_id = param_ti, population_c, NULL) as pop
from tb_town a left join
tb_country b on b.country_id = a.country_id;
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我来说两句