Relation:Tutorial 5
Projection
Project filters the table by columns. You specify the columns you want to keep
We reuse the table films.csv
Look at the code on the right and compare with the result.
Show only the title and the year
| film | year |
|---|---|
| A bout de souffle | 1960 |
| Tirez sur le pianiste | 1960 |
| Cléo de 5 à 7 | 1962 |
| Jules et Jim | 1962 |
| Pierrot le fou | 1965 |
| Week-End | 1967 |
| Die verlorene Ehre der Katharina Blum | 1975 |
| Der starke Ferdinand | 1976 |
| Sans toi ni loi | 1985 |
Show only the director
| director |
|---|
| Godard |
| Truffaut |
| Varda |
| von Trotta |
| Kluge |
You may notice we only have 4 rows instead of 9. This is because there are only 4 directors for these 9 films. In set theory, there cannot be duplicate values.
NB: In SQL you would get 9 rows, unless you use the DISTINCT option (which you should always).
Show the director first, then the title
| director | film |
|---|---|
| Godard | A bout de souffle |
| Truffaut | Tirez sur le pianiste |
| Varda | Cléo de 5 à 7 |
| Truffaut | Jules et Jim |
| Godard | Pierrot le fou |
| Godard | Week-End |
| von Trotta | Die verlorene Ehre der Katharina Blum |
| Kluge | Der starke Ferdinand |
| Varda | Sans toi ni loi |
Project allows you to reorder the columns, too.
Go to Tutorial 6
' ===Projection===
' Project filters the table by columns. You specify the columns you want to keep
' We reuse the table [[Media:films.csv]]
' Look at the code on the right and compare with the result.
' ''''Show only the title and the year'''''
read "films.csv"
project film, year
' '''''Show only the director'''''
read "films.csv"
project director
' You may notice we only have 4 rows instead of 9. This is because there are only 4 directors for these 9 films. In set theory, there cannot be duplicate values.
' NB: In SQL you would get 9 rows, unless you use the DISTINCT option (which you should always).
' '''''Show the director first, then the title'''''
read "films.csv"
project director, film
' Project allows you to reorder the columns, too.
' Go to [[Tutorial 6]]