References:
ADQL spec: http://www.ivoa.net/Documents/REC/ADQL/ADQL-20081030.pdf
Postgres data types: http://are.berkeley.edu/computing/help/manuals/postgres/c08.htm
JDBC data types (java.sql.Types)
SQL 92 grammar: http://savage.net.au/SQL/sql-92.bnf.html
SQL 99 grammar: http://savage.net.au/SQL/sql-99.bnf.html
SQL 2003 grammar: http://savage.net.au/SQL/sql-2003-2.bnf.html

datatypes inferred from ADQL spec' SQL reserved keywords 
using SQL 92 grammar for some inference on their usage:
-----------------------------------------------------------------------------------
BIT [[(L)]]
BIT VARYING [(L)]
CHAR [(L)]
CHARACTER [(L)] (?)
CHARACTER VARYING [(L)] (?)
DATE
DECIMAL [(L,S)]

DOUBLE PRECISION
FLOAT
IDENTITY (?)
INT
INTEGER
INTERVAL (?)

NCHAR [(L)]
NCHAR VARYING[(L)]
NATIONAL CHAR [(L)]
NATIONAL CHAR VARYING [(L)]
NATIONAL CHARACTER [(L)] (?)
NATIONAL CHARACTER VARYING [(L)] (?)

NUMERIC [(L,S)]
REAL
SMALLINT
TIME
TIMESTAMP
VARCHAR

SQL-92 grammar on datatypes
---------------------------
  <data type>    ::=
         <character string type> [ CHARACTER SET <character set specification> ]
     |     <national character string type>
     |     <bit string type>
     |     <numeric type>
     |     <datetime type>
     |     <interval type>

  <character string type>    ::=
         CHARACTER [ <left paren> <length> <right paren> ]
     |     CHAR [ <left paren> <length> <right paren> ]
     |     CHARACTER VARYING [ <left paren> <length> <right paren> ]
     |     CHAR VARYING [ <left paren> <length> <right paren> ]
     |     VARCHAR [ <left paren> <length> <right paren> ]

  <length>    ::=   <unsigned integer>

  <national character string type>    ::=
         NATIONAL CHARACTER [ <left paren> <length> <right paren> ]
     |     NATIONAL CHAR [ <left paren> <length> <right paren> ]
     |     NCHAR [ <left paren> <length> <right paren> ]
     |     NATIONAL CHARACTER VARYING [ <left paren> <length> <right paren> ]
     |     NATIONAL CHAR VARYING [ <left paren> <length> <right paren> ]
     |     NCHAR VARYING [ <left paren> <length> <right paren> ]

  <bit string type>    ::=
         BIT [ <left paren> <length> <right paren> ]
     |     BIT VARYING [ <left paren> <length> <right paren> ]

  <numeric type>    ::=
         <exact numeric type>
     |     <approximate numeric type>

  <exact numeric type>    ::=
         NUMERIC [ <left paren> <precision> [ <comma> <scale> ] <right paren> ]
     |     DECIMAL [ <left paren> <precision> [ <comma> <scale> ] <right paren> ]
     |     DEC [ <left paren> <precision> [ <comma> <scale> ] <right paren> ]
     |     INTEGER
     |     INT
     |     SMALLINT

  <precision>    ::=   <unsigned integer>

  <scale>    ::=   <unsigned integer>

  <approximate numeric type>    ::=
         FLOAT [ <left paren> <precision <right paren> ]
     |     REAL
     |     DOUBLE PRECISION

  <datetime type>    ::=
         DATE
     | TIME [ <left paren> <time precision> <right paren> ] [ WITH TIME ZONE ]
     | TIMESTAMP [ <left paren> <timestamp precision> <right paren> ] [ WITH TIME ZONE ]

  <time precision>    ::=   <time fractional seconds precision>

  <time fractional seconds precision>    ::=   <unsigned integer>

  <timestamp precision>    ::=   <time fractional seconds precision>

  <interval type>    ::=   INTERVAL <interval qualifier>

  <interval qualifier>    ::=
         <start field> TO <end field>
     | <single datetime field>

  <start field>    ::=
         <non-second datetime field> [ <left paren> <interval leading field precision> <right paren> ]

  <non-second datetime field>    ::=   YEAR | MONTH | DAY | HOUR | MINUTE

  <interval leading field precision>    ::=   <unsigned integer>

  <end field>    ::=
         <non-second datetime field>
     | SECOND [ <left paren> <interval fractional seconds precision> <right paren> ]

  <interval fractional seconds precision>    ::=   <unsigned integer>

  <single datetime field>    ::=
         <non-second datetime field> [ <left paren> <interval leading field precision> <right paren> ]
     | SECOND [ <left paren> <interval leading field precision> [ <comma> <left paren> <interval fractional seconds precision> ] <right paren> ] 




SQL 99 grammar on datatypes
---------------------------
  <data type>    ::=
         <predefined type>
     |     <row type>
     |     <user-defined type>
     |     <reference type>
     |     <collection type>

  <predefined type>    ::=
         <character string type> [ CHARACTER SET <character set specification> ]
     |     <national character string type>
     |     <binary large object string type>
     |     <bit string type>
     |     <numeric type>
     |     <boolean type>
     |     <datetime type>
     |     <interval type>

  <character string type>    ::=
         CHARACTER [ <left paren> <length> <right paren> ]
     |     CHAR [ <left paren> <length> <right paren> ]
     |     CHARACTER VARYING <left paren> <length> <right paren>
     |     CHAR VARYING <left paren> <length> <right paren>
     |     VARCHAR <left paren> <length> <right paren>
     |     CHARACTER LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     CHAR LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     CLOB [ <left paren> <large object length> <right paren> ]

  <length>    ::=   <unsigned integer>

  <unsigned integer>    ::=   <digit> ...

  <large object length>    ::=   <unsigned integer> [ <multiplier> ] | <large object length token>

  <multiplier>    ::=   K | M | G

  <large object length token>    ::=   <digit> ... <multiplier>

  <national character string type>    ::=
         NATIONAL CHARACTER [ <left paren> <length> <right paren> ]
     |     NATIONAL CHAR [ <left paren> <length> <right paren> ]
     |     NCHAR [ <left paren> <length> <right paren> ]
     |     NATIONAL CHARACTER VARYING <left paren> <length> <right paren>
     |     NATIONAL CHAR VARYING <left paren> <length> <right paren>
     |     NCHAR VARYING <left paren> <length> <right paren>
     |     NATIONAL CHARACTER LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     NCHAR LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     NCLOB [ <left paren> <large object length> <right paren> ]

  <binary large object string type>    ::=
         BINARY LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     BLOB [ <left paren> <large object length> <right paren> ]

  <bit string type>    ::=
         BIT [ <left paren> <length> <right paren> ]
     |     BIT VARYING <left paren> <length> <right paren>

  <numeric type>    ::=   <exact numeric type> | <approximate numeric type>

  <exact numeric type>    ::=
         NUMERIC [ <left paren> <precision> [ <comma> <scale> ] <right paren> ]
     |     DECIMAL [ <left paren> <precision> [ <comma> <scale> ] <right paren> ]
     |     DEC [ <left paren> <precision> [ <comma> <scale> ] <right paren> ]
     |     INTEGER
     |     INT
     |     SMALLINT

  <precision>    ::=   <unsigned integer>

  <scale>    ::=   <unsigned integer>

  <approximate numeric type>    ::=
         FLOAT [ <left paren> <precision> <right paren> ]
     |     REAL
     |     DOUBLE PRECISION

  <boolean type>    ::=   BOOLEAN

  <datetime type>    ::=
         DATE
     |     TIME [ <left paren> <time precision> <right paren> ] [ <with or without time zone> ]
     |     TIMESTAMP [ <left paren> <timestamp precision> <right paren> ] [ <with or without time zone> ]

  <time precision>    ::=   <time fractional seconds precision>

  <time fractional seconds precision>    ::=   <unsigned integer>

  <with or without time zone>    ::=   WITH TIME ZONE | WITHOUT TIME ZONE

  <timestamp precision>    ::=   <time fractional seconds precision>

  <interval type>    ::=   INTERVAL <interval qualifier>

  <interval qualifier>    ::=   <start field> TO <end field> | <single datetime field>

  <start field>    ::=
         <non-second primary datetime field> [ <left paren> <interval leading field precision> <right paren> ]

  <non-second primary datetime field>    ::=   YEAR | MONTH | DAY | HOUR | MINUTE

  <interval leading field precision>    ::=   <unsigned integer>

  <end field>    ::=
         <non-second primary datetime field>
     |     SECOND [ <left paren> <interval fractional seconds precision> <right paren> ]

  <interval fractional seconds precision>    ::=   <unsigned integer>

  <single datetime field>    ::=
         <non-second primary datetime field> [ <left paren> <interval leading field precision> <right paren> ]
     |     SECOND [ <left paren> <interval leading field precision> [ <comma> <interval fractional seconds precision> ] <right paren> ]

  <row type>    ::=   ROW <row type body>

  <row type body>    ::=   <left paren> <field definition> [ { <comma> <field definition> }... ] <right paren>



SQL 2003 <data type>
--------------------
 <data type>    ::=
         <predefined type>
     |     <row type>
     |     <path-resolved user-defined type name>
     |     <reference type>
     |     <collection type>

  <predefined type>    ::=
         <character string type> [ CHARACTER SET <character set specification> ] [ <collate clause> ]
     |     <national character string type> [ <collate clause> ]
     |     <binary large object string type>
     |     <numeric type>
     |     <boolean type>
     |     <datetime type>
     |     <interval type>

  <character string type>    ::=
         CHARACTER [ <left paren> <length> <right paren> ]
     |     CHAR [ <left paren> <length> <right paren> ]
     |     CHARACTER VARYING <left paren> <length> <right paren>
     |     CHAR VARYING <left paren> <length> <right paren>
     |     VARCHAR <left paren> <length> <right paren>
     |     CHARACTER LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     CHAR LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     CLOB [ <left paren> <large object length> <right paren> ]

  <national character string type>    ::=
         NATIONAL CHARACTER [ <left paren> <length> <right paren> ]
     |     NATIONAL CHAR [ <left paren> <length> <right paren> ]
     |     NCHAR [ <left paren> <length> <right paren> ]
     |     NATIONAL CHARACTER VARYING <left paren> <length> <right paren>
     |     NATIONAL CHAR VARYING <left paren> <length> <right paren>
     |     NCHAR VARYING <left paren> <length> <right paren>
     |     NATIONAL CHARACTER LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     NCHAR LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     NCLOB [ <left paren> <large object length> <right paren> ]

  <binary large object string type>    ::=
         BINARY LARGE OBJECT [ <left paren> <large object length> <right paren> ]
     |     BLOB [ <left paren> <large object length> <right paren> ]

  <numeric type>    ::=   <exact numeric type> | <approximate numeric type>

  <exact numeric type>    ::=
         NUMERIC [ <left paren> <precision> [ <comma> <scale> ] <right paren> ]
     |     DECIMAL [ <left paren> <precision> [ <comma> <scale> ] <right paren> ]
     |     DEC [ <left paren> <precision> [ <comma> <scale> ] <right paren> ]
     |     SMALLINT
     |     INTEGER
     |     INT
     |     BIGINT

  <approximate numeric type>    ::=
         FLOAT [ <left paren> <precision> <right paren> ]
     |     REAL
     |     DOUBLE PRECISION

  <length>    ::=   <unsigned integer>

  <large object length>    ::=
         <unsigned integer> [ <multiplier> ] [ <char length units> ]
     |     <large object length token> [ <char length units> ]

  <char length units>    ::=   CHARACTERS | CODE_UNITS | OCTETS

  <precision>    ::=   <unsigned integer>

  <scale>    ::=   <unsigned integer>

  <boolean type>    ::=   BOOLEAN

  <datetime type>    ::=
         DATE
     |     TIME [ <left paren> <time precision> <right paren> ] [ <with or without time zone> ]
     |     TIMESTAMP [ <left paren> <timestamp precision> <right paren> ] [ <with or without time zone> ]

  <with or without time zone>    ::=   WITH TIME ZONE | WITHOUT TIME ZONE

  <time precision>    ::=   <time fractional seconds precision>

  <timestamp precision>    ::=   <time fractional seconds precision>

  <time fractional seconds precision>    ::=   <unsigned integer>

  <interval type>    ::=   INTERVAL <interval qualifier>

  <row type>    ::=   ROW <row type body>

  <row type body>    ::=   <left paren> <field definition> [ { <comma> <field definition> }... ] <right paren>

  <reference type>    ::=   REF <left paren> <referenced type> <right paren> [ <scope clause> ]

  <scope clause>    ::=   SCOPE <table name>

  <referenced type>    ::=   <path-resolved user-defined type name>

  <path-resolved user-defined type name>    ::=   <user-defined type name>

  <path-resolved user-defined type name>    ::=   <user-defined type name>

  <collection type>    ::=   <array type> | <multiset type>

  <array type>    ::=   <data type> ARRAY [ <left bracket or trigraph> <unsigned integer> <right bracket or trigraph> ]

  <multiset type>    ::=   <data type> MULTISET