# SQL

SELECT x, y
FROM table_1
ORDER BY x, y DESC

# R

### order(X, na.last=TRUE, decreasing=FALSE)

na.last 控制空值NA排在最前还是最后，默认最后
desceasing 控制升序还是降序排列

`> #vector`
```> X <- c(7,4,5,2,8,1,9,3)
> order(X)
```
`[1] 6 4 8 2 3 1 5 7`
```> X[order(X)]
[1] 1 2 3 4 5 7 8 9> X[order(X, decreasing=TRUE)]
[1] 9 8 7 5 4 3 2 1 > order(-X) # '-' equals decreasing=TRUE[1] 7 5 1 3 2 4 8 6> #vector
> #dataframe.
> X <- c(7,4,5,3,8,1,9,3)
> Y <- c(50, 80, 30, 70, 20, 10, 40, 90)
> order(X, Y) #only print X's order, no Y's
[1] 6 4 8 2 3 1 5 7
> table_1 <- data.frame(x=X, y=Y)
> table_1
x  y
1 7 50
2 4 80
3 5 30
4 3 70
5 8 20
6 1 10
7 9 40
8 3 90> order(table_1\$x, table_1\$y) #X asc, Y asc, print the row number's sequence
[1] 6 4 8 2 3 1 5 7> table_1[order(table_1\$x, -table_1\$y),] #X asc, Y desc  x  y
6 1 10
8 3 904 3 70
2 4 80
3 5 30
1 7 50
5 8 20
7 9 40> table_1[order(-table_1\$x, table_1\$y), ] #X desc, Y asc
x  y
7 9 40
5 8 20
1 7 50
3 5 30
2 4 80
4 3 70
8 3 90
6 1 10```

```> table_1[order(-table_1\$x, -table_1\$y), ] #X desc, Y asc
```
```  x  y
7 9 40
5 8 20
1 7 50
3 5 30
2 4 80
8 3 90
4 3 70
6 1 10```

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