Relations

Here is a relation literal. It has two parts, each between braces. It has a heading and a body.

{     day_seq:int, day_name:str}{
tuple{day_seq:=1,  day_name:="Monday"},
tuple{day_seq:=2,  day_name:="Tuesday"},
tuple{day_seq:=3,  day_name:="Wednesday"},
tuple{day_seq:=4,  day_name:="Thursday"},
tuple{day_seq:=5,  day_name:="Friday"},
tuple{day_seq:=6,  day_name:="Saturday"},
tuple{day_seq:=7,  day_name:="Sunday"},
}

┌─────────┬───────────┐
│ day_seq │ day_name  │
├─────────┼───────────┤
│       1 │ Monday    │
│       2 │ Tuesday   │
│       3 │ Wednesday │
│       4 │ Thursday  │
│       5 │ Friday    │
│       6 │ Saturday  │
│       7 │ Sunday    │
└─────────┴───────────┘

The heading is a set of attributes: day_seq and day_name in the example above. Each attribute has a name and a type. Currently available types include:

• bool (true/false)
• int (64 bit)
• float (64 bit)
• str
• time
• tuple{...}
• {...} (i.e. a relation)

The body is a set of tuples. A tuple is a set of attribute names and typed values.

Here's a relation literal with a shorthand for the body tuples to simplify typing. This relies on the left-to-right ordering of the values in square brackets aligning with the left-to-right ordering of the heading, but only for loading the relation from the script: after that is has no left-right ordering.

{month_seq:int, month_name:str}{
[1,             "January"],
[2,             "February"],
[3,             "March"],
[4,             "April"],
[5,             "May"],
[6,             "June"],
[7,             "July"],
[8,             "August"],
[9,             "September"],
[10,            "October"],
[11,            "November"],
[12,            "December"],
}

┌───────────┬────────────┐
│ month_seq │ month_name │
├───────────┼────────────┤
│         1 │ January    │
│         2 │ February   │
│         3 │ March      │
│         4 │ April      │
│         5 │ May        │
│         6 │ June       │
│         7 │ July       │
│         8 │ August     │
│         9 │ September  │
│        10 │ October    │
│        11 │ November   │
│        12 │ December   │
└───────────┴────────────┘

There are two pre-defined relations named dee and dum which are the ones with no attributes: dee has one tuple, dum has none.

dee

┌┐
││
├┤
││
└┘

dum

┌┐
││
├┤
└┘

Later we'll see how we can use dee in another shorthand to construct single-tuple relations.