    This file contains a BNF definition of ADQL, the Astronomical
    Data Query Language. The elements are arranged in alphabetical
    order. ADQL is based upon a subset of SQL92 with extensions for
    astronomical usage.

    The definition reflects the ADQL spec version v2.0
    The select statement is found at <query_specification>
    For region and associated constructs, see...
    <geometry_value_expression>,
    <numeric_geometry_function>,
    <string_geometry_function>
    User defined function is found at <user_defined_function>
    See SQL92 for a similar page describing SQL92 in full.

      <ADQL_language_character> ::=
          <simple_Latin_letter>
        | <digit>
        | <SQL_special_character>

      <ADQL_reserved_word> ::=
          ABS
        | ACOS
        | AREA
        | ASIN
        | ATAN
        | ATAN2
        | BOX
        | CEILING
        | CENTROID
        | CIRCLE
        | CONTAINS
        | COORD1
        | COORD2
        | COORDSYS
        | COS
        | DEGREES
        | DISTANCE
        | EXP
        | FLOOR
        | INTERSECTS
        | LOG
        | LOG10
        | MOD
        | PI
        | POINT
        | POLYGON
        | POWER
        | RADIANS
        | REGION
        | RAND
        | ROUND
        | SIN
        | SQRT
        | TOP
        | TAN
        | TRUNCATE

      <SQL_embedded_language_character> ::=
          <left_bracket>
        | <right_bracket>

      <SQL_reserved_word> ::=
         ABSOLUTE | ACTION | ADD | ALL
       | ALLOCATE | ALTER | AND
       | ANY | ARE
       | AS | ASC
       | ASSERTION | AT
       | AUTHORIZATION | AVG
       | BEGIN | BETWEEN | BIT | BIT_LENGTH
       | BOTH | BY
       | CASCADE | CASCADED | CASE | CAST
       | CATALOG
       | CHAR | CHARACTER | CHAR_LENGTH
       | CHARACTER_LENGTH | CHECK | CLOSE | COALESCE
       | COLLATE | COLLATION
       | COLUMN | COMMIT
       | CONNECT
       | CONNECTION | CONSTRAINT
       | CONSTRAINTS | CONTINUE
       | CONVERT | CORRESPONDING | COUNT | CREATE | CROSS
       | CURRENT
       | CURRENT_DATE | CURRENT_TIME
       | CURRENT_TIMESTAMP | CURRENT_USER | CURSOR
       | DATE | DAY | DEALLOCATE
       | DECIMAL | DECLARE | DEFAULT | DEFERRABLE
       | DEFERRED | DELETE | DESC | DESCRIBE | DESCRIPTOR
       | DIAGNOSTICS
       | DISCONNECT | DISTINCT | DOMAIN | DOUBLE | DROP
       | ELSE | END | END-EXEC | ESCAPE
       | EXCEPT | EXCEPTION
       | EXEC | EXECUTE | EXISTS
       | EXTERNAL | EXTRACT
       | FALSE | FETCH | FIRST | FLOAT | FOR
       | FOREIGN | FOUND | FROM | FULL
       | GET | GLOBAL | GO | GOTO
       | GRANT | GROUP
       | HAVING | HOUR
       | IDENTITY | IMMEDIATE | IN | INDICATOR
       | INITIALLY | INNER | INPUT
       | INSENSITIVE | INSERT | INT | INTEGER | INTERSECT
       | INTERVAL | INTO | IS
       | ISOLATION
       | JOIN
       | KEY
       | LANGUAGE | LAST | LEADING | LEFT
       | LEVEL | LIKE | LOCAL | LOWER
       | MATCH | MAX | MIN | MINUTE | MODULE
       | MONTH
       | NAMES | NATIONAL | NATURAL | NCHAR | NEXT | NO
       | NOT | NULL
       | NULLIF | NUMERIC
       | OCTET_LENGTH | OF
       | ON | ONLY | OPEN | OPTION | OR
       | ORDER | OUTER
       | OUTPUT | OVERLAPS
       | PAD | PARTIAL | POSITION | PRECISION | PREPARE
       | PRESERVE | PRIMARY
       | PRIOR | PRIVILEGES | PROCEDURE | PUBLIC
       | READ | REAL | REFERENCES | RELATIVE | RESTRICT
       | REVOKE | RIGHT
       | ROLLBACK | ROWS
       | SCHEMA | SCROLL | SECOND | SECTION
       | SELECT
       | SESSION | SESSION_USER | SET
       | SIZE | SMALLINT | SOME | SPACE | SQL | SQLCODE
       | SQLERROR | SQLSTATE
       | SUBSTRING | SUM | SYSTEM_USER
       | TABLE | TEMPORARY
       | THEN | TIME | TIMESTAMP
       | TIMEZONE_HOUR | TIMEZONE_MINUTE
       | TO | TRAILING | TRANSACTION
       | TRANSLATE | TRANSLATION | TRIM | TRUE
       | UNION | UNIQUE | UNKNOWN | UPDATE | UPPER | USAGE
       | USER | USING
       | VALUE | VALUES | VARCHAR | VARYING | VIEW
       | WHEN | WHENEVER | WHERE | WITH | WORK | WRITE
       | YEAR
       | ZONE

      <SQL_special_character> ::=
         <space>
       | <double_quote>
       | <percent>
       | <ampersand>
       | <quote>
       | <left_paren>
       | <right_paren>
       | <asterisk>
       | <plus_sign>
       | <comma>
       | <minus_sign>
       | <period>
       | <solidus>
       | <colon>
       | <semicolon>
       | <less_than_operator>
       | <equals_operator>
       | <greater_than_operator>
       | <question_mark>
       | <underscore>
       | <vertical_bar>

      <ampersand> ::= &

      <approximate_numeric_literal> ::= <mantissa>E<exponent>

      <area> ::= AREA <left_paren> <geometry_value_expression> <right_paren>

      <as_clause> ::= [ AS ] <column_name>

      <asterisk> ::= *

      <between_predicate> ::=
         <value_expression> [ NOT ] BETWEEN
         <value_expression> AND <value_expression>

      <boolean_factor> ::= [ NOT ] <boolean_primary>

      <boolean_primary> ::=
         | <left_paren> <search_condition> <right_paren>
           <predicate>

      <boolean_term> ::=
          <boolean_factor>
        | <boolean_term> AND <boolean_factor>

      <box> ::=
          BOX <left_paren> <coord_sys>
                         <comma> <coordinates>
                         <comma> <numeric_value_expression>
                         <comma> <numeric_value_expression>
                    <right_paren>

      <catalog_name> ::= <identifier>

      <centroid> ::= CENTROID <left_paren> <geometry_value_expression> <right_paren>

      <character_factor> ::= <character_primary>
      !! For information only, SQL92 supports <collate_clause>

      <character_primary> ::=
          <value_expression_primary>
        | <string_value_function>

      <character_representation> ::= <nonquote_character> | <quote_symbol>
      !! A way of allowing a single quote to be escaped by a single quote.

      <character_string_literal> ::=
         <quote> [ <character_representation>... ] <quote>
         [ { <separator>... <quote> [ <character_representation>... ] <quote> }... ]

      <character_value_expression> ::= <concatenation> | <character_factor>

      <circle> ::=
          CIRCLE <left_paren> <coord_sys>
                      <comma> <coordinates>
                      <comma> <radius>
                 <right_paren>

      <colon> ::= :

      <column_name> ::= <identifier>

      <column_name_list> ::= <column_name> [ { <comma> <column_name> }... ]

      <column_reference> ::= [ <qualifier> <period> ] <column_name>

      <comma> ::= ,

      <comment> ::= <comment_introducer> [ <comment_character>... ] <newline>

      <comment_character> ::= <nonquote_character> | <quote>

      <comment_introducer> ::= <minus_sign><minus_sign> [<minus_sign>...]

      <comp_op> ::=
          <equals_operator>
        | <not_equals_operator>
        | <less_than_operator>
        | <greater_than_operator>
        | <less_than_or_equals_operator>
        | <greater_than_or_equals_operator>

      <comparison_predicate> ::=
          <value_expression> <comp_op> <value_expression>

      <concatenation> ::= <character_value_expression> <concatenation_operator> <character_factor>

      <concatenation_operator> ::= ||

      <contains> ::= CONTAINS <left_paren> <geometry_value_expression> <comma> <geometry_value_expression> <right_paren>

      <coord1> ::= COORD1 <left_paren> <coord_value> <right_paren>

      <coord2> ::= COORD2 <left_paren> <coord_value> <right_paren>

      <coord_sys> ::= <string_value_expression>

      <coord_value> ::= <point> | <column_reference>

      <coordinate1> ::= <numeric_value_expression>

      <coordinate2> ::= <numeric_value_expression>

      <coordinates> ::=  <coordinate1>  <comma>  <coordinate2>

      <correlation_name> ::= <identifier>

      <correlation_specification> ::= [ AS ] <correlation_name>

      <default_function_prefix> ::=
       !! The prefix is set by default to "udf_".
       !! It should be possible to change the default prefix to accommodate local preferences.

      <delimited_identifier> ::= <double_quote> <delimited_identifier_body> <double_quote>
      !! These diagrams are somewhat difficult to follow through and understand immediately.
      !! The idea is to allow any identifier to be quoted by enclosing within double quotes.
      !! This can allow the use of reserved words as identifiers, eg: "DATE" as a column name.
      !! The identifier can also contain double quotes as long as they are escaped by double quotes.
      !! For example: "Table""X" will be identifier Table"X

      <delimited_identifier_body> ::= <delimited_identifier_part>...

      <delimited_identifier_part> ::= <nondoublequote_character> | <double_quote_symbol>

      <delimiter_token> ::=
            <character_string_literal>
        |   <delimited_identifier>
        |   <SQL_special_character>
        |   <not_equals_operator>
        |   <greater_than_or_equals_operator>
        |   <less_than_or_equals_operator>
        |   <concatenation_operator>
        |   <double_period>
        |   <left_bracket>
        |   <right_bracket>

      <derived_column> ::= <value_expression> [ <as_clause> ]

      <derived_table> ::= <table_subquery>

      <digit> ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

      <distance> ::=
         DISTANCE <left_paren> <coord_value> <comma> <coord_value> <right_paren>

      <double_period> ::= ..

      <double_quote> ::= "

      <double_quote_symbol> ::= <double_quote><double_quote>

      <equals_operator> ::= =

      <exact_numeric_literal> ::=
          <unsigned_integer> [ <period> [ <unsigned_integer> ] ]
        | <period> <unsigned_integer>

      <exists_predicate> ::= EXISTS <table_subquery>

      <exponent> ::= <signed_integer>

      <extract_coordsys> ::= COORDSYS <left_paren> <geometry_value_expression> <right_paren>

      <factor> ::= [ <sign> ] <numeric_primary>

      <from_clause> ::= FROM <table_reference>
         [ { <comma> <table_reference> }... ]

      <general_literal> ::= <character_string_literal>
      !! ADQL Note:
      !! For information, SQL92 has <general_literal>, and also supports
      !! <national_character_string_literal>, <bit_string_literal>,
      !! <hex_string_literal>, <datetime_literal> and <interval_literal>
      !! Good to retain this as a place-holder, bearing in mind
      !! that we might need <bit_string_literal> and <hex_string_literal>
      !! at some point in the future?

      <general_set_function> ::=
         <set_function_type> <left_paren> [ <set_quantifier> ] <value_expression> <right_paren>

      <geometry_value_expression> ::= <value_expression_primary> | <geometry_value_function>

      <geometry_value_function> ::=
           <box>
         | <centroid>
         | <circle>
         | <point>
         | <polygon>
         | <region>

      <greater_than_operator> ::= >

      <greater_than_or_equals_operator> ::= >=

      <group_by_clause> ::= GROUP BY <grouping_column_reference_list>

      <grouping_column_reference> ::= <column_reference>
      !! For information, SQL92 supports a <collate_clause>

      <grouping_column_reference_list> ::=
          <grouping_column_reference> [ { <comma> <grouping_column_reference> }... ]

      <having_clause> ::= HAVING <search_condition>

      <identifier> ::= <regular_identifier> | <delimited_identifier>

      <in_predicate> ::=
          <value_expression> [ NOT ] IN <in_predicate_value>

      <in_predicate_value> ::=
         <table_subquery> | <left_paren> <in_value_list> <right_paren>

      <in_value_list> ::=
          <value_expression> { <comma> <value_expression> } ...

      <intersects> ::= INTERSECTS <left_paren> <geometry_value_expression> <comma> <geometry_value_expression> <right_paren>

      <join_column_list> ::= <column_name_list>

      <join_condition> ::= ON <search_condition>

      <join_specification> ::= <join_condition> | <named_columns_join>

      <join_type> ::=
         INNER
       | <outer_join_type> [ OUTER ]
      !! For information, SQL92 also supports UNION

      <joined_table> ::=
          <qualified_join>
        | <left_paren> <joined_table> <right_paren>

      <keyword> ::= <SQL_reserved_word> | <ADQL_reserved_word>

      <left_bracket> ::= [

      <left_paren> ::= (

      <less_than_operator> ::= <

      <less_than_or_equals_operator> ::= <=

      <like_predicate> ::=
          <match_value> [ NOT ] LIKE <pattern>

      <mantissa> ::= <exact_numeric_literal>

      <match_value> ::= <character_value_expression>

      <math_function> ::=
          ABS <left_paren> <numeric_value_expression> <right_paren>
    	  | CEILING <left_paren> <numeric_value_expression> <right_paren>
    	  | DEGREES <left_paren> <numeric_value_expression> <right_paren>
    	  | EXP <left_paren> <numeric_value_expression> <right_paren>
    	  | FLOOR <left_paren> <numeric_value_expression> <right_paren>
    	  | LOG <left_paren> <numeric_value_expression> <right_paren>
    	  | LOG10 <left_paren> <numeric_value_expression> <right_paren>
    	  | MOD <left_paren> <numeric_value_expression> <comma> <numeric_value_expression> <right_paren>
    	  | PI <left_paren><right_paren>
    	  | POWER <left_paren> <numeric_value_expression> <comma> <numeric_value_expression> <right_paren>
    	  | RADIANS <left_paren> <numeric_value_expression> <right_paren>
    	  | RAND <left_paren> [ <numeric_value_expression> ] <right_paren>
    	  | ROUND <left_paren> <numeric_value_expression> [<comma> <signed_integer>] <right_paren>
    	  | SQRT <left_paren> <numeric_value_expression> <right_paren>
    	  | TRUNCATE <left_paren> <numeric_value_expression> [<comma> <signed_integer>] <right_paren>

      <minor_radius> ::= <numeric_value_expression>

      <minus_sign> ::= -

      <named_columns_join> ::= USING <left_paren> <join_column_list> <right_paren>

      <newline> ::=
      !! Implementation defined end of line indicator

      <non_predicate_geometry_function> ::=
         <area>
       | <coord1>
       | <coord2>
       | <distance>

      <nondelimiter_token> ::=
          <regular_identifier>
        | <keyword>
        | <unsigned_numeric_literal>
       !! For information, SQL92 has some others.
       !! (Jeff: Not sure I understand how this is used.)

      <nondoublequote_character> ::=
       !! See SQL92 syntax rules. But basically what it says.

      <nonquote_character> ::=
      !! One ASCII character but not a single quote

      <not_equals_operator> ::= <not_equals_operator1> | <not_equals_operator2>

      <not_equals_operator1> ::= <>

      <not_equals_operator2> ::= !=

      <null_predicate> ::= <column_reference> IS [ NOT ] NULL

      <numeric_geometry_function> ::=
          <predicate_geometry_function> | <non_predicate_geometry_function>

      <numeric_primary> ::=
          <value_expression_primary>
        | <numeric_value_function>

      <numeric_value_expression> ::=
          <term>
        | <numeric_value_expression> <plus_sign> <term>
        | <numeric_value_expression> <minus_sign> <term>

      <numeric_value_function> ::=
         <trig_function>
       | <math_function>
       | <numeric_geometry_function>
       | <user_defined_function>
      !! For information, SQ92 also supports <position_expression>,
      !! <extract_expression> and <length_expression>

      <order_by_clause> ::= ORDER BY <sort_specification_list>

      <ordering_specification> ::= ASC | DESC

      <outer_join_type> ::= LEFT | RIGHT | FULL

      <pattern> ::= <character_value_expression>

      <percent> ::= %

      <period> ::= .

      <plus_sign> ::= +

      <point> ::= POINT <left_paren> <coord_sys> <comma> <coordinates> <right_paren>

      <polygon> ::=
          POLYGON <left_paren> <coord_sys>
                       <comma> <coordinates>
                       <comma> <coordinates>
                     { <comma> <coordinates> } ?
                  <right_paren>

      <predicate> ::=
         <comparison_predicate>
       | <between_predicate>
       | <in_predicate>
       | <like_predicate>
       | <null_predicate>
       | <exists_predicate>
      !! For information, SQL92 also supports the following predicates:
      !! <quantified_comparison_predicate>, <unique_predicate>,
      !! <match_predicate> and <overlaps_predicate>

      <predicate_geometry_function> ::= <contains> | <intersects>

      <qualified_join> ::=
          <table_reference> [ NATURAL ] [ <join_type> ] JOIN
          <table_reference> [ <join_specification> ]

      <qualifier> ::= <table_name> | <correlation_name>

      <query_expression> ::=
           <query_specification>
         | <joined_table>
       !! ADQL Note: SQL92 uses <non_join_query_expression> rather than <query_specification>

      <query_specification> ::=
          SELECT [ <set_quantifier> ] [ <set_limit> ] <select_list> <table_expression>

      <question_mark> ::= ?

      <quote> ::= '

      <quote_symbol> ::= <quote> <quote>

      <radius> ::= <numeric_value_expression>

      <region> ::= REGION <left_paren> <string_value_expression> <right_paren>

      <regular_identifier> ::=
          <simple_Latin_letter>...
          [ { <digit> | <simple_Latin_letter> | <underscore> }... ]

      <right_bracket> ::= ]

      <right_paren> ::= )

      <schema_name> ::= [ <catalog_name> <period> ] <unqualified_schema name>

      <search_condition> ::=
          <boolean_term>
        | <search_condition> OR <boolean_term>

      <select_list> ::=
          <asterisk>
        | <select_sublist> [ { <comma> <select_sublist> }... ]

      <select_sublist> ::= <derived_column> | <qualifier> <period> <asterisk>

      <semicolon> ::= ;

      <separator> ::= { <comment> | <space> | <newline> }...

      <set_function_specification> ::=
          COUNT <left_paren> <asterisk> <right_paren>
        | <general_set_function>

      <set_function_type> ::= AVG | MAX | MIN | SUM | COUNT

      <set_limit> ::= TOP <unsigned_integer>

      <set_quantifier> ::= DISTINCT | ALL

      <sign> ::= <plus_sign> | <minus_sign>

      <signed_integer> ::= [ <sign> ] <unsigned_integer>

      <simple_Latin_letter> ::=
          <simple_Latin_upper_case_letter>
        | <simple_Latin_lower_case_letter>

      <simple_Latin_lower_case_letter> ::=
          a | b | c | d | e | f | g | h | i | j | k | l | m | n | o
        | p | q | r | s | t | u | v | w | x | y | z

      <simple_Latin_upper_case_letter> ::=
          A | B | C | D | E | F | G | H | I | J | K | L | M | N | O
        | P | Q | R | S | T | U | V | W | X | Y | Z

      <solidus> ::= /

      <sort_key> ::= <column_name> | <unsigned_integer>
       !! For information, the use of <unsigned_integer> in <sort_key>is a deprecated feature of SQL92

      <sort_specification> ::=
          <sort_key> [ <ordering_specification> ]
      !! For information, SQL92 also supports <collate_clause>

      <sort_specification_list> ::=
          <sort_specification> [ { <comma> <sort_specification> }... ]

      <space> ::=
      !! Imagine there is a space character here

      <string_geometry_function> ::= <extract_coordsys>

      <string_value_expression> ::=
          <character_value_expression>
      !! For information, SQL92 also supports <bit_value_expression>

      <string_value_function> ::= <string_geometry_function> | <user_defined_function>

      <subquery> ::= <left_paren> <query_expression> <right_paren>

      <table_expression> ::=
          <from_clause>
          [ <where_clause> ]
          [ <group_by_clause> ]
          [ <having_clause> ]
          [ <order_by_clause> ]

      <table_name> ::= [ <schema_name> <period> ] <identifier>

      <table_reference> ::=
         <table_name> [ <correlation_specification> ]
       | <derived_table> <correlation_specification>
       | <joined_table>

      <table_subquery> ::= <subquery>

      <term> ::=
          <factor>
        | <term> <asterisk> <factor>
        | <term> <solidus> <factor>

      <token> ::=
          <nondelimiter_token>
        | <delimiter_token>

      <trig_function> ::=
          ACOS <left_paren> <numeric_value_expression> <right_paren>
        | ASIN <left_paren> <numeric_value_expression> <right_paren>
        | ATAN <left_paren> <numeric_value_expression> <right_paren>
        | ATAN2 <left_paren> <numeric_value_expression> <comma> <numeric_value_expression> <right_paren>
        | COS <left_paren> <numeric_value_expression> <right_paren>
        | COT <left_paren> <numeric_value_expression> <right_paren>
        | SIN <left_paren> <numeric_value_expression> <right_paren>
        | TAN <left_paren> <numeric_value_expression> <right_paren>

      <underscore> ::= _

      <unqualified_schema name> ::= <identifier>

      <unsigned_integer> ::= <digit>...

      <unsigned_literal> ::= <unsigned_numeric_literal> | <general_literal>

      <unsigned_numeric_literal> ::=
         <exact_numeric_literal>
       | <approximate_numeric_literal>

      <unsigned_value_specification> ::= <unsigned_literal>

      <user_defined_function> ::=
          <user_defined_function_name>
              <left_paren>
                  [ <user_defined_function_param> [ { <comma> <user_defined_function_param> }... ] ]
              <right_paren>
      !! ADQL Note:
      !! If metadata on a user defined function is available, this should be used.
      !! For example, function names and cardinality of arguments should be checked.

      <user_defined_function_name> ::=
           [ <default_function_prefix> ] <regular_identifier>
       !! Function names should be checked against metadata where available.

      <user_defined_function_param> ::= <value_expression>

      <value_expression> ::=
          <numeric_value_expression>
        | <string_value_expression>
        | <geometry_value_expression>

      <value_expression_primary> ::=
          <unsigned_value_specification>
        | <column_reference>
        | <set_function_specification>
        | <left_paren> <value_expression> <right_paren>
      !! For information, SQL92 supports <scalar_subquery>,
      !! <case_expression> and <cast_specification>

      <vertical_bar> ::= |

      <where_clause> ::= WHERE <search_condition>