MySQL visitor supporting REPLACE INTO). q.v. the relevant sections of this
specification for details.
+=head2 Dialect-agnostic construction
+
+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 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
There are two major components to SQL::Abstract v2.
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'. If a _query value is unrecognized by the
-Visitor, the Visitor is expected to throw an error.
+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
=over 4
-=item * _name
+=item * type
This indicates the structural unit that this hash is representing. While this
specification provides for standard structural units, different Visitors may
The hash will be structured as follows:
{
- _name => 'Identifier',
- items => [Scalar],
+ type => 'Identifier',
+ element1 => Scalar,
+ element2 => Scalar,
+ element3 => Scalar,
}
+If element3 exists, then element2 must exist. element1 must always exist. If a
+given element exists, then it must be defined and of non-zero length.
+
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. It may either be a:
+A Value is a Perl scalar. Depending on the type, a Visitor may be able to make
+certain decisions.
=over 4
=item * String
-A String is a quoted series of characters
+A String is a quoted series of characters. The Visitor is expected to ensure
+that embedded quotes are properly handled per the SQL dialect's quoting scheme.
=item * Number
-A Number is an unquoted number in some numeric format
+A Number is an unquoted number in some numeric format.
=item * Null
quoted in such a fashion so as to protect against SQL injection attacks. (q.v.
L<DBI/quote()> for an example.)
+BindParameters are normally represented by a '?'.
+
=back
The hash will be structured as follows:
{
- _name => 'Value'
- _subtype => [ 'String' | 'Number' | 'Null' | 'BindParameter' ]
- value => [Scalar]
+ type => 'Value'
+ subtype => [ 'String' | 'Number' | 'Null' | 'BindParameter' ]
+ value => Scalar
}
The provided subtypes are the ones that all Visitors are expected to support.
Visitors may choose to support additional subtypes. Visitors are expected to
throw an exception upon encountering an unknown subtype.
-=head3 Function
-
-A Function is anything of the form C< name( arglist ) > where C<name> is a
-string and C<arglist> is a comma-separated list of Expressions.
+=head3 Operator
-Yes, a Subquery is legal as an argument for many functions. Some example
-functions are:
+An Operator would be, in SQL dialect terms, a unary operator, a binary operator,
+a trinary operator, or a function. Since different dialects may have a given
+functionality as an operator or a function (such as CONCAT in MySQl vs. || in
+Oracle for string concatenation), they will be represented in the AST as generic
+operators.
-=over 4
-
-=item * C<< MAX >>
-
-=item * C<< MIN >>
-
-=item * C<< SUM >>
-
-=item * C<< IF >>
+The hash will be structured as follows:
-=back
+ {
+ type => 'Operator',
+ op => String,
+ args => ExpressionList,
+ }
-Functions have a cardinality, or expected number of arguments. Some functions,
+Operators have a cardinality, or expected number of arguments. Some operators,
such as MAX(), have a cardinality of 1. Others, such as IF(), have a cardinality
of N, meaning they can have any number of arguments greater than 0. Others, such
-as NOW(), have a cardinality of 0. Several functions with the same meaning may
+as NOW(), have a cardinality of 0. Several operators with the same meaning may
have a different cardinality in different SQL dialects as different engines may
-allow different behaviors.
+allow different behaviors. As cardinality may differ between dialects, enforcing
+cardinality is necessarily left to the Visitor.
+
+Operators also have restrictions on the types of arguments they will accept. The
+first argument may or may not restricted in the same fashion as the other
+arguments. As with cardinality, this restriction will need to be managed by the
+Visitor.
-As cardinality may differ between dialects, enforcing cardinality is necessarily
-left to the Visitor.
+The operator name needs to take into account the possibility that the RDBMS may
+allow UDFs (User-Defined Functions) that have the same name as an operator, such
+as 'AND'. This will have to be managed by the Visitor.
=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
single-row restriction is much more difficult and, in most cases, probably
impossible.
-Subqueries, when expressed in SQL, must bounded by parentheses.
+Subqueries, when expressed in SQL, must be bounded by parentheses.
-=head3 Unary Operator
-
-A UnaryOperator takes a single argument on the RHS. The argument for a
-UnaryOperator is an Expression.
+=head3 Expression
-Visitors are expected to support, at minimum, the following operators:
+An Expression can be any one of the following:
=over 4
-=item * NOT X
+=item * Identifier
-=item * ANY X
+=item * Value
-=item * ALL X
+=item * Operator
-=item * SOME X
+=item * Subquery
=back
-The hash for a UnaryOperator is as follows:
-
- {
- _name => 'UnaryOperator'
- _operator => [ .... ],
- argument1 => Expression,
- }
-
-Visitors may choose to support additional operators. Visitors are expected to
-throw an exception upon encountering an unknown operator.
+An Expression is a meta-syntactic unit. An "Expression" unit will never appear
+within the AST. It acts as a junction.
-=head3 BinaryOperator
+=head3 ExpressionList
-A BinaryOperator takes two arguments (one on the LHS and one on the RHS). The
-arguments for a BinaryOperator are all Expressions.
+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.
-Visitors are expected to support, at minimum, the following operators:
-
-=over 4
-
-=item * X = Y
-
-=item * X != Y
-
-=item * X > Y
-
-=item * X < Y
-
-=item * X >= Y
-
-=item * X <= Y
-
-=item * X IS Y
-
-=item * X IN Y
-
-=item * X NOT IN Y
-
-=item * X AND Y
-
-=item * X OR Y
-
-=back
-
-(Note that an operator can comprise of what would be multiple tokens in a normal
-parsing effort.)
-
-Visitors may choose to support additional operators. Visitors are expected to
-throw an exception upon encountering an unknown operator.
-
-The hash for a BinaryOperator is as follows:
+The hash for an ExpressionList is as follows:
{
- _name => 'BinaryOperator'
- _operator => [ .... ],
- argument1 => Expression,
- argument2 => Expression,
+ type => 'ExpressionList',
+ separator => ',',
+ elements => Array of Expressions,
}
-=head3 TrinaryOperator
-
-A TrinaryOperator takes three arguments. It generally is composed of two
-elements with one argument to the LHS, one to the RHS, and a third in the middle
-of the elements. The arguments for a TrinaryOperator are all Expressions.
-
-Visitors are expected to support, at minimum, the following operators:
-
-=over 4
-
-=item * X BETWEEN Y AND Z
-
-=back
+An ExpressionList is always rendered in SQL with parentheses around it.
-Visitors may choose to support additional operators. Visitors are expected to
-throw an exception upon encountering an unknown operator.
+=head3 Nesting
-The hash for a TrinaryOperator is as follows:
-
- {
- _name => 'TrinaryOperator'
- _operator => [ .... ],
- argument1 => Expression,
- argument2 => Expression,
- argument3 => Expression,
- }
-
-=head3 Expression
-
-An expression can be any one of the following:
-
-=over 4
-
-=item * Value
-
-=item * Function
-
-=item * Subquery
-
-=item * UnaryOperator
-
-=item * BinaryOperator
-
-=item * TrinaryOperator
-
-=item * ( Expression )
-
-=back
-
-Parentheses indicate precedence and, in some situations, are necessary for
-certain operators.
-
-The hash for an Expression is as follows:
-
- {
- _name => 'Expression',
- _subtype => [ 'Value' | 'Function' | 'SubQuery' | . . . ],
- }
+There is no specific operator or nodetype for nesting. Instead, nesting is
+explicitly specified by node descent in the AST.
=head2 SQL clauses
This corresponds to the SELECT clause of a SELECT statement.
-A select clause is composed as follows:
+A select clause unit is an array of one or more SelectComponent units.
- SelectComponent := Expression [ [ AS ] String ]
+The hash for a SelectComponent unit is composed as follows:
- SelectComponent
- [ , SelectComponent ]*
+ {
+ type => 'SelectComponent',
+ value => Expression,
+ as => String,
+ }
+
+The 'as' component is optional. Visitors may choose to make it required in
+certain situations.
=head3 tables
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.
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.
-A table clause is composed as follows:
+A TableJoin is a junction of the following elements:
- TableIdentifier := Identifier [ [ AS ] String ]
- JoinType := < LEFT|RIGHT [ OUTER ] > | INNER | CROSS
+=over 4
- TableIdentifier
- [
- < , TableIdentifier >
- | <
- [ JoinType ] JOIN TableIdentifier
- [
- < USING ( Identifier [ , Identifier ] ) >
- | < ON [ ( ] Expression [ , Expression ] [ ) ] >
- ]
- >
- ]*
+=item * TableIdentifier
-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.
+=item * Operator
-=head3 where
+=back
-This corresponds to the WHERE clause in a SELECT, UPDATE, or DELETE statement.
+The hash for a TableIdentifier will be composed as follows:
+
+ # TableIdentifier
+ {
+ type => 'TableIdentifier',
+ value => Expression,
+ as => String,
+ }
+
+The value should be either an Identifier or a SubQuery.
+
+The hash for an Operator within a tables clause will be composed as follows:
-A where clause is composed as follows:
+ # Operator
+ {
+ type => 'Operator',
+ op => '< LEFT|RIGHT|FULL [ OUTER ] > | INNER | CROSS',
+ on => Expression,
+ }
+
+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.
- WhereOperator := AND | OR
- WhereExpression := Expression | Expression WhereOperator Expression
+=head3 where
+
+This corresponds to the WHERE clause in a SELECT, UPDATE, or DELETE statement.
- WhereExpression
+A where clause is composed of an Expression.
=head3 set
This corresponds to the optional list of columns in an INSERT statement.
-A columns clause is composed as follows:
+A columns clause is an IdentifierList and the unit is composed as follows:
- ( Identifier [ , Identifier ]* )
+ columns => [
+ Identifier,
+ [ Identifier, ]*
+ ],
=head3 values
This corresponds to the VALUES clause in an INSERT statement.
-A values clause is composed as follows:
+A values clause is an ExpressionList and the unit is composed as follows.
- ( Expression [ , Expression ]* )
+ values => [
+ Expression,
+ [ Expression, ]*
+ ],
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.
Identifier, WhereExpression
+=head1 TODO
+
+=over 4
+
+=item * sproc unit
+
+=back
+
=head1 AUTHORS
robkinyon: Rob Kinyon C<< <rkinyon@cpan.org> >>
projects / dbsrgits/SQL-Abstract-2.0-ish.git / blobdiff