The AST will not attempt to be immediately readable to a human as SQL. In fact,
due to the dialect differences, particularly in terms of which use operators and
-which use functions for a given action, the AST will ...
-
-XXX FILL ME IN LATER XXX
+which use functions for a given action, the AST will provide simple units. It is
+the responsibility of the Visitor to provide the appropriate SQL. Furthermore,
+the AST will be very generic and only provide hints for a subset of SQL. If a
+Visitor is sufficiently intelligent, pretty SQL may be emitted, but that is not
+the goal of this AST.
=head1 COMPONENTS
The AST will be a HoHo..oH (hash of hash of ... of hashes). The keys to the
outermost hash will be the various clauses of a SQL statement, plus some
-metadata keys. All metadata keys will be identifiable as such by being prefixed
-with an underscore. All keys will be in lowercase.
+metadata keys.
=head2 Metadata keys
These are the additional metadata keys that the AST provides for.
-=head3 _query
+=head3 type
This denotes what kind of query this AST should be interpreted as. Different
-Visitors may accept additional values for _query. For example, a MySQL Visitor
-may choose to accept 'replace' for REPLACE INTO. If a _query value is
+Visitors may accept additional values for type. For example, a MySQL Visitor
+may choose to accept 'replace' for REPLACE INTO. If a type value is
unrecognized by the Visitor, the Visitor is expected to throw an error.
-All Visitors are expected to handle the following values for _query:
+All Visitors are expected to handle the following values for type:
=over 4
=back
-=head3 _version
+=head3 ast_version
This denotes the version of the AST. Different versions will indicate different
-capabilities provided. Visitors will choose to respect the _version as needed
+capabilities provided. Visitors will choose to respect the ast_version as needed
and desired.
=head2 Structural units
Visitors are expected to, by default, quote all identifiers according to the SQL
dialect's quoting scheme.
+Any of the elements may be '*', as in SELECT * or SELECT COUNT(*). Visitors must
+be careful to I<not> quote asterisks.
+
=head3 Value
A Value is a Perl scalar. Depending on the type, a Visitor may be able to make
=head3 Subquery
-A Subquery is another AST whose _query metadata parameter is set to "SELECT".
+A Subquery is another AST whose type metadata parameter is set to "SELECT".
Most places that a Subquery can be used would require a single value to be
returned (single column, single row), but that is not something that the AST can
An ExpressionList is a list of Expressions, generally separated by commas
(though other separators may be appropriate at times or for different SQL
-dialects).
+dialects). An null separator may also be used.
The hash for an ExpressionList is as follows:
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,
+ }
+
=head2 SQL clauses
These are all the legal and acceptable clauses within the AST that would
{
type => 'SelectComponent',
value => Expression,
- [ as => Identifier, ]
+ as => String,
}
The 'as' component is optional. Visitors may choose to make it required in
This is a list of tables that this clause is affecting. It corresponds to the
FROM clause in a SELECT statement and the INSERT INTO/UPDATE/DELETE clauses in
-those respective statements. Depending on the _query metadata entry, the
+those respective statements. Depending on the type metadata entry, the
appropriate clause name will be used.
-A tables clause unit is an array of one or more TableComponent units.
-
The tables clause has several RDBMS-specific variations. The AST will support
all of them and it is up to the Visitor object constructing the actual SQL to
validate and/or use what is provided as appropriate.
-The hash for a TableJoin will be composed as follows:
+A TableJoin is a junction of the following elements:
- # TableJoin
- {
- type => 'TableJoin',
- join => < LEFT|RIGHT [ OUTER ] > | INNER | CROSS | ',',
- [ using => IdentifierList, ]
- [ on => ExpressionList, ]
- }
+=over 4
-A TableJoin may not have both a 'using' element and an 'on' element. It may
-have one of them if the 'join' element is not equal to ',' but doesn't have to.
-If the 'join' element is equal to ',', then it may not have either a 'using' or
-an 'on' element.
+=item * TableIdentifier
+
+=item * Operator
+
+=back
The hash for a TableIdentifier will be composed as follows:
# TableIdentifier
{
type => 'TableIdentifier',
- value => Identifier | SubQuery
- [ join => TableJoin, ]
- [ as => Identifier, ]
+ value => Expression,
+ as => String,
}
-The first TableComponent in a tables clause may not have a join element. All
-other TableComponent elements that do not have a join element will have a
-default join element of:
+The value should be either an Identifier or a SubQuery.
+
+The hash for an Operator within a tables clause will be composed as follows:
+ # Operator
{
- type => 'TableJoin',
- join => ',',
+ type => 'Operator',
+ op => '< LEFT|RIGHT|FULL [ OUTER ] > | INNER | CROSS',
+ on => Expression,
}
-The 'as' component is optional. Visitors may choose to make it required in
-certain situations (such as MySQL requiring an alias for subqueries).
-
-Additionally, where aliases are provided for in the TableIdentifier, those
-aliases must be used as the tablename in subsequent Identifiers that identify a
-column of that table. This may be enforceable by the AST or the Visitor. But, it
-is more likely that it will not be.
+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.
=head3 where
This corresponds to the WHERE clause in a SELECT, UPDATE, or DELETE statement.
-A where clause is composed as follows:
-
- WhereOperator := AND | OR
- WhereExpression := Expression | Expression WhereOperator Expression
-
- WhereExpression
+A where clause is composed of an Expression.
=head3 set
Identifier, WhereExpression
-=head1 EXAMPLES
-
-The following are example SQL statements and a possible AST for each one.
+=head1 TODO
=over 4
-=item * SELECT 1
-
- {
- _query => 'select',
- _ast_version => 0.0001,
- select => [
- {
- type => 'SelectComponent',
- value => {
- type => 'Value',
- subtype => 'number',
- value => 1,
- },
- },
- ],
- }
-
-=item * SELECT NOW() AS time FROM dual AS duality
-
- {
- _query => 'select',
- _ast_version => 0.0001,
- select => [
- {
- type => 'SelectComponent',
- value => {
- type => 'Function',
- function => 'NOW',
- },
- as => {
- type => 'Identifier',
- element1 => 'time',
- },
- },
- ],
- tables => [
- {
- type => 'TablesComponent',
- value => {
- type => 'Identifier',
- element1 => 'dual',
- },
- as => {
- type => 'Identifier',
- element1 => 'duality',
- },
- },
- ],
- }
+=item * sproc unit
=back
projects / dbsrgits/SQL-Abstract-2.0-ish.git / blobdiff