urQL/docs/query.md

```
<query> ::=
[WITH <common-table-expression> ]
FROM { [<ship-qualifer>]<table-view> [ [AS] <alias> ]
       [ { JOIN | LEFT JOIN | RIGHT JOIN | OUTER JOIN [ALL] }
         <ship-qualifer><table-view> [ [AS] <alias> ]
         ON <predicate>
       ]
     } [ ,...n ]
[ WHERE <predicate> ]
SELECT [ TOP <n> ] [ DISTINCT ]
  { * 
    | {
        { [<ship-qualifer>]<table-view> | <alias> }. ] *
        | <expression> [ [ AS ] column_alias ]
        | column_alias = expression
      } [ ,...n ]
  }
[ GROUP BY { <column> | <column-ordinal>  } [ ,...n ] ]
[ HAVING <predicate> ]
[ INTO <new-table> ]
[ ORDER BY { <column> | <column-ordinal>  } [ ,...n ] ]
[ { UNION [ WITH DUPS ] 
    | EXCEPT 
    | INTERSECT 
    | DIVIDED BY [ WITH REMAINDER ] 
    | CROSS JOIN [ ( { { 1 | 2 }:{ * | 1..n } } ) ] } <query> ] [ ...n ]
```

```
<predicate> ::= 
  { [ NOT ] <predicate> | ( <simple-predicate> ) }
  [ { { AND | OR } [ NOT ] { <predicate> | ( <simple-predicate> ) }
      [ ...n ]
  ]
```

```
<simple-predicate> ::=
  { expression <binary-operator> expression
    | expression [ NOT ] BETWEEN expression AND expression
    | expression IS [ NOT ] NULL
    | expression IS [ NOT ] DISTINCT FROM expression
    | expression [ NOT ] IN
      ( { <one-column-query> ) | expression [ ,...n ] } )
    | expression <binary-operator> { ALL | ANY} ( <one-column-query> )
    | EXISTS ( <query> ) }
```

```
<expression> ::=
  {
    constant
    | <scalar-function>
    | <column>
    | [ <unary-operator> ] <expression>
    | <expression> <binary-operator> <expression>
  }
```

```
<binary-operator> ::=
  { = | <> | != | > | >= | !> | < | <= | !< }
```

```
`<column> ::=
  { [ { <alias>. | <table-view>. } ]<column-name>
    | <constant> 
    | <column-alias> }
```

```
<scalar-function> ::=
  IF <predicate> THEN <expression> ELSE <expression> ENDIF
  | CASE <expression>`
    WHEN { <predicate> | <expression> } THEN <expression> [ ...n ]
    [ ELSE <expression> ]
    END
  | COALESCE ( <expression> [ ,...n ] )
  | native hoon (stretch goal)
```

Discussion:
Not shown in diagrams, parentheses distinguish order of operations for binary conjunctions `AND` and `OR`.

Set operators apply the previous result set to the next query unless otherwise qualified by parentheses.

`ORDER BY` is not allowed in Common Table Experessions (CTE, WITH clause) or in any query joined by set operators except for the last of the queries.

`SELECT INTO` targets an existing table not otherwise in the query.

`COALESCE` returns the first `<expression>` in the list that does not evaluate to `~` (in the case of unit) or not in the selected `<expression>` due to `LEFT` or `RIGHT JOIN`.

If a `CASE WHEN` expression is a `<predicate>`, the expected boolean (or loobean) logic applies. If it is a <expression> atom value 0 is treated as false and any other value as true (not loobean).

Cross database joins are allowed, but not cross ship joins.

`DISTINCT FROM` is like equals, `=`, except comparing two nulls will yield false.