=head3 Value
-A Value is a Perl scalar. Depending on the type, a Visitor may be able to make
-certain decisions.
+A Value is a Perl scalar. Depending on the subtype, a Visitor may be able to
+make certain decisions. The following are the minimally-valid subtypes:
=over 4
{
type => 'Operator',
op => String,
- args => ExpressionList,
+ args => [
+ Expression,
+ ],
}
Operators have a cardinality, or expected number of arguments. Some operators,
An Expression is a meta-syntactic unit. An "Expression" unit will never appear
within the AST. It acts as a junction.
-=head3 ExpressionList
-
-An ExpressionList is a list of Expressions, generally separated by commas
-(though other separators may be appropriate at times or for different SQL
-dialects). An null separator may also be used.
-
-The hash for an ExpressionList is as follows:
-
- {
- type => 'ExpressionList',
- separator => ',',
- elements => Array of Expressions,
- }
-
-An ExpressionList is always rendered in SQL with parentheses around it.
-
=head3 Nesting
-A Nesting is, essentially, another set of parentheses.
-
-The hash for a Nesting is as follows:
-
- {
- type => 'Nesting',
- args => Array of Expressions,
- }
+There is no specific operator or nodetype for nesting. Instead, nesting is
+explicitly specified by node descent in the AST.
=head2 SQL clauses
}
A USING clause is syntactic sugar for an ON clause and, as such, is not provided
-for by the AST. A join of a comma is identical to a CROSS JOIN. The on clause is
-optional.
+for by the AST. A join of a comma is identical to a CROSS JOIN and, as such, is
+not provided for by the AST. The on clause is optional.
=head3 where
This corresponds to the SET clause in an INSERT or UPDATE statement.
-A set clause is composed as follows:
+A set clause unit is an array of one or more SetComponent units.
- SetComponent := Identifier = Expression
+The hash for SetComponent unit is composed as follows:
- SetComponent [ , SetComponent ]*
+ {
+ type => 'SetComponent',
+ col => Identifier,
+ value => Expression,
+ }
=head3 columns
This corresponds to the optional list of columns in an INSERT statement.
-A columns clause is an IdentifierList and the unit is composed as follows:
-
- columns => [
- Identifier,
- [ Identifier, ]*
- ],
+A columns clause unit is an array of one or more Identifier units.
=head3 values
This corresponds to the VALUES clause in an INSERT statement.
-A values clause is an ExpressionList and the unit is composed as follows.
-
- values => [
- Expression,
- [ Expression, ]*
- ],
+A values clause unit is an array of one or more Expression units.
If there is a columns clause, the number of entries in the values clause must be
equal to the number of entries in the columns clause.
This corresponds to the ORDER BY clause in a SELECT statement.
-An orderby clause is composed as follows:
+A orderby clause unit is an array of one or more OrderbyComponent units.
+
+The hash for a OrderbyComponent unit is composed as follows:
- OrderByComponent := XXX-TODO-XXX
- OrderByDirection := ASC | DESC
+ {
+ type => 'OrderbyComponent',
+ value => < Identifier | Number >
+ dir => '< ASC | DESC >',
+ }
- OrderByComponent [ OrderByDirection ]
- [ , OrderByComponent [ OrderByDirection ] ]*
+The dir element, if omitted, will be defaulted to ASC by the AST. The number
+corresponds to a column in the select clause.
=head3 groupby
This corresponds to the GROUP BY clause in a SELECT statement.
-An groupby clause is composed as follows:
+A groupby clause unit is an array of one or more GroupbyComponent units.
- GroupByComponent := XXX-TODO-XXX
+The hash for a GroupbyComponent unit is composed as follows:
- GroupByComponent [ , GroupByComponent ]*
+ {
+ type => 'GroupbyComponent',
+ value => < Identifier | Number >
+ }
+
+The number corresponds to a column in the select clause.
=head3 rows
This corresponds to the clause that is used in some RDBMS engines to limit the
number of rows returned by a query. In MySQL, this would be the LIMIT clause.
-A rows clause is composed as follows:
+The hash for a rows clause is composed as follows:
+
+ {
+ start => Number,
+ count => Number,
+ }
- Number [, Number ]
+The start attribute, if ommitted, will default to 0. The count attribute is
+optional.
=head3 for
This corresponds to the clause that is used in some RDBMS engines to indicate
what locks are to be taken by this SELECT statement.
-A for clause is composed as follows:
+The hash for a for clause is composed as follows:
- UPDATE | DELETE
+ {
+ value => '< UPDATE | DELETE >',
+ }
=head3 connectby
This corresponds to the clause that is used in some RDBMS engines to provide for
an adjacency-list query.
-A connectby clause is composed as follows:
+The hash for a for clause is composed as follows:
+
+ {
+ start_with => [
+ Expression,
+ ],
+ connect_by => {
+ option => '< PRIOR | NOCYCLE >'
+ cond => [
+ Expression,
+ ],
+ },
+ order_siblings => orderby-clause,
+ }
- Identifier, WhereExpression
+Both the start_with and order_siblings clauses are optional.
=head1 TODO
projects / dbsrgits/SQL-Abstract-2.0-ish.git / blobdiff