[英]MySQL Subquery to count multiple columns with GROUP BY
我的桌子
+---------+----------+---+
| id | a1 | a2 | a3 |
+---------+----+----+----+
| 1 | 1 | 0 | 0 |
| 2 | 0 | 1 | 0 |
| 3 | 1 | 1 | 1 |
| 4 | 1 | 1 | 0 |
+---------+----+----+----+
結果是我想要的:梅賽德斯3寶馬3福特1大眾2
查詢我試過..
SELECT
IF(a1=1,'Mercedes',
IF(a2=1,'BMW',
IF(a3=1,'Ford',
IF(a4=1,'VW',
'NO')))) AS marke,
COUNT(autos.id) AS anzahl FROM autos
WHERE autos.land=de GROUP BY marke ORDER BY anzahl DESC
我得到了預期的結果,但是只有第一行才算正確。 如何添加子查詢來再次查詢同一表,顯示每個字段(a1,a2,a3)的正確計數
我還會嘗試什么:以下子查詢也失敗!
SELECT
IF(a1=1,'Mercedes',
IF(a2=1,'BMW',
IF(a3=1,'Ford',
IF(a4=1,'VW',
'NO')))) AS marke,
IF(a1=1,(SELECT COUNT( autos.id) FROM marke WHERE a1=1),
IF(a2=1,(SELECT COUNT( autos.id) FROM marke WHERE a2=1),
IF(a3=1,(SELECT COUNT( autos.id) FROM marke WHERE a3=1),
IF(a4=1,(SELECT COUNT( autos.id) FROM marke WHERE a4=1),
'NO')))) AS anzahl,
FROM autos
WHERE autos.land=de GROUP BY marke ORDER BY anzahl DESC
希望這使我的問題更容易理解。
在每種汽車上都使用列是設計表格的一種不好的方法,因為它使數據的處理方式與您所經歷的方式完全相同。
沒有每個品牌都有專欄; 有一列將每輛車鏈接到特定品牌:
CREATE TABLE car_makes (
make_id bigint unsigned not null auto_increment primary key,
name varchar(64)
);
CREATE TABLE cars (
car_id bigint unsigned not null auto_increment primary key,
make_id bigint
);
INSERT INTO car_makes (name) VALUES ('Ford'), ('VW'), ('BMW'), ('Mercedes');
/* now let's create some cars that match your desired results */
INSERT INTO cars (make_id) SELECT make_id FROM car_makes;
INSERT INTO cars (make_id) SELECT make_id FROM car_makes WHERE name IN('VW', 'Mercedes', 'BMW');
INSERT INTO cars (make_id) SELECT make_id FROM car_makes WHERE name IN( 'Mercedes', 'BMW');
現在,您可以根據需要簡單地按品牌分組:
SELECT name , count(*) from cars
JOIN car_makes ON ( car_makes.make_id = cars.make_id)
GROUP BY car_makes.make_id;
您會看到這如何幫助簡化數據管理,並使查詢效率更高。
+----------+----------+
| name | count(*) |
+----------+----------+
| Ford | 1 |
| VW | 2 |
| BMW | 3 |
| Mercedes | 3 |
+----------+----------+
從汽車中選擇SUM(a1)AS'Mercedes',sum(a2)AS'BMW',sum(a3)AS'FORD'
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