消除重複和檢索最高值爲每個ID

Question

我有這樣的一個表：

ID  Signal Station Owner 
111  -120  Home  M1 
111  -120  Home  M1 
111  -120  Home  M2 
111  -120  Car  M1 
111  -120  Car  M2 
111  -120  Work  M1 
111 -120  Dept  M3 
111  -130  Car  M1 
111  -135  Work  M2 
222  -98  Home  M2 
222  -95  Work  M1 
222  -103  Work  M2 

我只需要查詢爲每個ID返回最大信號：如果信號等於顯示一個在random.But如果Signal對於多個工作站和所有者是相同的，則以下查詢將返回重複項。請幫我出去this.All領域都在同一個表

ID Signal Station Owner 
111 -120  Dept  M3  
111 -120  Home  M1  
111 -120  Work  M2  
222 -95  Work  M1 

但我需要進行重複的條目

Here is the SQL: 

SELECT g.ID, g.MaxSignal, g.Station, g.OwnerID FROM (SELECT id, MAX(Signal) AS 
MaxSignal FROM t GROUP BY id) AS g inner join t ON g.id = t.id AND g.MaxSignal = t.Signal; 

Answer 1

我想你可以使用：

SELECT `ID`, MAX(`Signal`), `Station`, `OwnerID` FROM `table_name` GROUP BY `ID` 

代替您的查詢

Answer 2

第一次選擇後嘗試將不同：

SELECT DISTINCT g.ID, g.MaxSignal, t.Station, t.OwnerID 
FROM 
(
    SELECT id, MAX(Signal) AS MaxSignal 
    FROM t 
    GROUP BY id 
) AS g 
INNER JOIN t ON g.id = t.id AND g.MaxSignal = t.Signal; 

這適用於顯示的示例數據，但不適用於行具有相同ID和（最大）信號但行站或所有者或兩者具有不同值的行。在SQL Server中我會避開這個問題，通過使用ROW_COUNT功能（有沒有在MySQL同等的功能？）：

SELECT Id, MaxSignal, Station, OwnerID 
FROM 
(
    SELECT 
     g.ID, 
     g.MaxSignal, 
     t.Station, 
     t.OwnerID , 
     ROW_NUMBER() OVER(PARTITION BY g.ID, g,MaxSignal ORDER BY t.Station) AS RowNumber 
    FROM 
    (
     SELECT id, MAX(Signal) AS MaxSignal 
     FROM t 
     GROUP BY id 
    ) AS g 
    INNER JOIN t ON g.id = t.id AND g.MaxSignal = t.Signal 
) AS T1 
WHERE RowNumber = 1 

Answer 3

SELECT DISTINCT g.ID, g.MaxSignal, t.Station, t.OwnerID 
FROM (SELECT id, MAX(Signal) AS MaxSignal 
     FROM t 
     GROUP BY id) AS g 
    INNER JOIN t 
     ON g.id = t.id 
      AND g.MaxSignal = t.Signal; 

Answer 4

以下是你需要查詢：

SELECT DISTINCT B.* FROM 
(SELECT ID,`Signal`,MIN(CONCAT(Station,'-',Owner)) MaxStationOwner 
FROM (SELECT DISTINCT t.* FROM 
(SELECT ID,MAX(`Signal`) `Signal` FROM t GROUP BY ID) AAA 
LEFT JOIN t USING (ID,`Signal`)) AA 
GROUP BY ID,`Signal`) A 
INNER JOIN t B 
ON A.MaxStationOwner=CONCAT(B.Station,'-',B.Owner) 
AND A.ID=B.ID AND A.`Signal`=B.`Signal`; 

這裏是您的樣本數據：

drop database if exists preeti; 
create database preeti; 
use preeti 
create table t 
(ID int not null, 
`Signal` int not null, 
Station varchar(10), 
Owner varchar(10)); 
insert into t values 
(111,  -120 ,  'Home' , 'M1'), 
(111,  -120 ,  'Home' , 'M1'), 
(111,  -120 ,  'Home' , 'M2'), 
(111,  -120 ,  'Car' , 'M1'), 
(111,  -120 ,  'Car' , 'M2'), 
(111,  -120 ,  'Work' , 'M1'), 
(111, -120 ,  'Dept' , 'M3'), 
(111,  -130 ,  'Car' , 'M1'), 
(111,  -135 ,  'Work' , 'M2'), 
(222,  -98 ,  'Home' , 'M2'), 
(222,  -95 ,  'Work' , 'M1'), 
(222,  -103 ,  'Work' , 'M2'); 

這裏被裝載示例數據：

mysql> drop database if exists preeti; 
Query OK, 1 row affected (0.03 sec) 

mysql> create database preeti; 
Query OK, 1 row affected (0.00 sec) 

mysql> use preeti 
Database changed 
mysql> create table t 
    -> (ID int not null, 
    -> `Signal` int not null, 
    -> Station varchar(10), 
    -> Owner varchar(10)); 
Query OK, 0 rows affected (0.06 sec) 

mysql> insert into t values 
    -> (111,  -120 ,  'Home' , 'M1'), 
    -> (111,  -120 ,  'Home' , 'M1'), 
    -> (111,  -120 ,  'Home' , 'M2'), 
    -> (111,  -120 ,  'Car' , 'M1'), 
    -> (111,  -120 ,  'Car' , 'M2'), 
    -> (111,  -120 ,  'Work' , 'M1'), 
    -> (111, -120 ,  'Dept' , 'M3'), 
    -> (111,  -130 ,  'Car' , 'M1'), 
    -> (111,  -135 ,  'Work' , 'M2'), 
    -> (222,  -98 ,  'Home' , 'M2'), 
    -> (222,  -95 ,  'Work' , 'M1'), 
    -> (222,  -103 ,  'Work' , 'M2'); 
Query OK, 12 rows affected (0.06 sec) 
Records: 12 Duplicates: 0 Warnings: 0 

mysql> 

這裏是輸出：

mysql> SELECT DISTINCT B.* FROM 
    -> (SELECT ID,`Signal`,MIN(CONCAT(Station,'-',Owner)) MaxStationOwner 
    -> FROM (SELECT DISTINCT t.* FROM 
    -> (SELECT ID,MAX(`Signal`) `Signal` FROM t GROUP BY ID) AAA 
    -> LEFT JOIN t USING (ID,`Signal`)) AA 
    -> GROUP BY ID,`Signal`) A 
    -> INNER JOIN t B 
    -> ON A.MaxStationOwner=CONCAT(B.Station,'-',B.Owner) 
    -> AND A.ID=B.ID AND A.`Signal`=B.`Signal`; 
+-----+--------+---------+-------+ 
| ID | Signal | Station | Owner | 
+-----+--------+---------+-------+ 
| 111 | -120 | Car  | M1 | 
| 222 | -95 | Work | M1 | 
+-----+--------+---------+-------+ 
2 rows in set (0.02 sec) 

mysql> 

試試看！

CAVEAT

請確保您有在表t這個索引：

ALTER TABLE t ADD INDEX ID_Signal_Index (ID,`Signal`);