# 2020/6/29 高レイヤー勉強会
## SQL勉強会
[SQL zoo]
https://sqlzoo.net/wiki/SELECT_within_SELECT_Tutorial
***SELECT_within_SELECT_Tutorial***の7～１０。
***Nested SELECT Quiz***
https://sqlzoo.net/wiki/SUM_and_COUNT の***SUM and COUNT***の１～８。

### h3 SELECT_within_SELECT_Tutorialの解答
>7
>SELECT continent, name, population FROM world x
WHERE population >= ALL
(SELECT population FROM world y
WHERE y.continent=x.continent
AND population>0)

ALL　(SELECT　・・・)でリストから特定の要素のみを比較したりできる。

>8
>select
continent, min(name)
from
world
group by
continent;

GROUP BY グループ化する要素名
で指定した要素でグループ化を行える。
表示は、指定したグループの中で集計した結果が表示される。

>9
>SELECT
name,continent,population
FROM
world A
WHERE
25000000>=ALL(SELECT population
FROM world B
WHERE B.continent=A.continent);

>10
>select
name, continent
from
world A
where
population>all(select 3*population
from world B
where B.continent= A.continent
and B.name <> A.name);

### h3　SUM and COUNT　解答
>1
>select
sum(population)
from
world;
sum(カラム名)

でカラムの数値を合計した値を表示

>2
>select
distinct(continent)
from
world;

distinct(カラム名)
で重複無しでカラムを表示

>3
>select
sum(gdp)
from
world
where
continent = 'Africa';

>4
>select
sum(gdp)
from
world
where
continent = 'Africa';

>5
>select
sum(population)
from
world
where
name in ('Estonia', 'Latvia', 'Lithuania');

>6
>select
continent, count(name)
from
world
group by
continent;

count(カラム名)
で

>7
>select
continent, count(name)
from
world
where
population >= 10000000
group by
continent;

>8
>select
continent
from
world
group by
continent
having
sum(population) >= 100000000;

### h3今回学習したSQLの語法
#### h4ALL

#### h4 GROUP BY

#### h4ALL
#### h4ALL
#### h4ALL
#### h4ALL
#### h4ALL
#### h4ALL