/* Context-free grammar for Doctrine Query Language
 *
 * Document syntax:
 *  - non-terminals begin with an upper case character
 *  - terminals begin with a lower case character
 *  - parentheses (...) are used for grouping
 *  - square brackets [...] are used for defining an optional part, eg. zero or
 *    one time
 *  - curly brackets {...} are used for repetion, eg. zero or more times
 *  - double quotation marks "..." define a terminal string
 *  - a vertical bar | represents an alternative
 *
 * At a first glance we'll support SQL-99 based queries
 * Initially Select and Sub-select DQL will not support LIMIT and OFFSET (due to limit-subquery algorithm)
 */

QueryLanguage   ::= SelectStatement | UpdateStatement | DeleteStatement

SelectStatement ::= SelectClause FromClause [WhereClause] [GroupByClause] [HavingClause] [OrderByClause]
UpdateStatement ::= UpdateClause [WhereClause]
DeleteStatement ::= DeleteClause [WhereClause]

Subselect       ::= SimpleSelectClause FromClause [WhereClause] [GroupByClause] [HavingClause] [OrderByClause]
SelectClause    ::= "SELECT" ["ALL" | "DISTINCT"] SelectExpression {"," SelectExpression}*
SimpleSelectClause ::= "SELECT" ["ALL" | "DISTINCT"] SelectExpression
DeleteClause    ::= "DELETE" ["FROM"] VariableDeclaration
WhereClause     ::= "WHERE" ConditionalExpression
FromClause      ::= "FROM" IdentificationVariableDeclaration {"," IdentificationVariableDeclaration}*
HavingClause    ::= "HAVING" ConditionalExpression
GroupByClause   ::= "GROUP" "BY" GroupByItem {"," GroupByItem}*
OrderByClause   ::= "ORDER" "BY" OrderByItem {"," OrderByItem}*
LimitClause     ::= "LIMIT" integer
OffsetClause    ::= "OFFSET" integer
UpdateClause    ::= "UPDATE" VariableDeclaration "SET" UpdateItem {"," UpdateItem}*

OrderByItem ::= Expression ["ASC" | "DESC"]
GroupByItem ::= PathExpression
UpdateItem ::= PathExpression "=" (Expression | "NULL")

IdentificationVariableDeclaration ::= RangeVariableDeclaration [IndexBy] {JoinVariableDeclaration}*
JoinVariableDeclaration ::= Join [IndexBy]
RangeVariableDeclaration ::= identifier {"." identifier}* [["AS"] IdentificationVariable]
VariableDeclaration ::= identifier [["AS"] IdentificationVariable]
IdentificationVariable ::= identifier

Join ::= ["LEFT" | "INNER"] "JOIN" RangeVariableDeclaration [("ON" | "WITH") ConditionalExpression]
IndexBy ::= "INDEX" "BY" identifier

ConditionalExpression ::= ConditionalTerm {"OR" ConditionalTerm}*
ConditionalTerm       ::= ConditionalFactor {"AND" ConditionalFactor}*
ConditionalFactor     ::= ["NOT"] ConditionalPrimary
ConditionalPrimary    ::= SimpleConditionalExpression | "(" ConditionalExpression ")"
SimpleConditionalExpression
                      ::= Expression (ComparisonExpression | BetweenExpression | LikeExpression
                      | InExpression | NullComparisonExpression) | ExistsExpression

Atom ::= string | integer | float | boolean | input_parameter

Expression ::= Term {("+" | "-") Term}*
Term       ::= Factor {("*" | "/") Factor}*
Factor     ::= [("+" | "-")] Primary
Primary    ::= PathExpression | Atom | "(" Expression ")" | Function | AggregateExpression

SelectExpression  ::= (PathExpressionEndingWithAsterisk | Expression | "(" Subselect ")" ) [["AS"] FieldIdentificationVariable]
PathExpression ::= identifier {"." identifier}*
PathExpressionEndingWithAsterisk ::= {identifier "."}* "*"
FieldIdentificationVariable ::= identifier

AggregateExpression ::= ("AVG" | "MAX" | "MIN" | "SUM") "(" ["DISTINCT"] Expression ")"
                    | "COUNT" "(" ["DISTINCT"] (Expression | "*") ")"

QuantifiedExpression     ::= ("ALL" | "ANY" | "SOME") "(" Subselect ")"
BetweenExpression        ::= ["NOT"] "BETWEEN" Expression "AND" Expression
ComparisonExpression     ::= ComparisonOperator ( QuantifiedExpression | Expression | "(" Subselect ")" )
InExpression             ::= ["NOT"] "IN" "(" (Atom {"," Atom}* | Subselect) ")"
LikeExpression           ::= ["NOT"] "LIKE" Expression ["ESCAPE" string]
NullComparisonExpression ::= "IS" ["NOT"] "NULL"
ExistsExpression         ::= "EXISTS" "(" Subselect ")"

ComparisonOperator ::= "=" | "<" | "<=" | "<>" | ">" | ">=" | "!="

Function ::= identifier "(" [Expression {"," Expression}*] ")"