Overview of SQL datataypes based on SQL 2003 (as it seems most extensive). "o" in column implies it exists also in other SQL versions, is anticipated by ADQL through its list reserved words. The columns JDBC and VOTable give the mapping to those two type systems. A "[(P[,S])]" after a datatypeps indicates that a precision (P) and possibly a scale(S) can be provided.

For info on database support look at JVO presentation during Victoria 2006 interop. Also various JDBC mapping tables such as this.

SQL 2003	SQL 92	SQL 99	ADQL 2.0	JDBC type4	VOTable 1.2 (beta)
CHARACTER [(P)]	o	o	o	CHAR	char
CHAR [(P)]	o	o	o	CHAR	char
CHARACTER VARYING[(P)]	o	o	o	VARCHAR	char
CHAR VARYING [(P)]	o	o	o	VARCHAR	char
VARCHAR [(P)]	o	o	o	VARCHAR	char
CHARACTER LARGE OBJECT [(P)]1	x	o	x	CLOB	char (?)
CHAR LARGE OBJECT [(P)]1	x	o	x	CLOB	char (?)
CLOB [(P)]1	x	o	x	CLOB	char (?)
NATIONAL CHARACTER [(P)]	o	o	o	NCHAR	char
NATIONAL CHAR [(P)]	o	o	o	NCHAR	char
NCHAR [(P)]	o	o	o	NCHAR	char
NATIONAL CHARACTER VARYING[(P)]	o	o	o	NVARCHAR	char
NATIONAL CHAR VARYING [(P)]	o	o	o	NVARCHAR	char
NCHAR VARYING [(P)]	o	o	o	NVARCHAR	char
NATIONAL CHARACTER LARGE OBJECT [(P)]1	x	o	x	NCLOB	char (?)
NCHAR LARGE OBJECT [(P)]1	x	o	x	NCLOB	char (?)
NCLOB [(P)]1	x	o	x	NCLOB	char (?)
BINARY LARGE OBJECT [(P)]1	x	o	x	BLOB	unsignedByte6
BLOB [(P)]1	x	o	x	BLOB	unsignedByte6
NUMERIC [(P[,S])]	o	o	o	NUMERIC	x5
DECIMAL [(P[,S])]	o	o	o	DECIMAL	x5
DEC [(P[,S])]	o	o	x	DECIMAL	x5
INTEGER	o	o	o	INTEGER	int
INT	o	o	o	INTEGER	int
SMALLINT	o	o	o	SMALLINT	short
BIGINT	x	x	x	BIGINT	long
FLOAT [(P)]	o	o	o	FLOAT	double/float
REAL	o	o	o	REAL	float
DOUBLE PRECISION	o	o	o	DOUBLE	double
BOOLEAN	x	o	x	BOOLEAN	boolean
DATE	o	o	o	DATE	x
TIME [(P)]2	o	o	o	TIME	x
TIMESTAMP [(P)]2	o	o	o	TIMESTAMP	x
INTERVAL ... 3	o	o	o	x	x
x	BIT [(P)]	o	o	BIT?	bit?
x	BIT VARYING [(P)]	o	o	BIT?	bit?
x	x	x	STC	x	x
x	x	x	x	x	floatComplex
x	x	x	x	x	doubleComplex
x	x	x	x	x	unicodeChar

¹ The syntax for sizes of large objects is actually somewhat different from the "[(P)]" applicable to simpler data types.
² The syntax for sizes of TIME and TIMESTAMP is actually somewhat different from the "[(P)]" applicable to simpler data types.
³ See the SQL 2003 grammar for precise specification of INTERVAL type.
⁴ JDBC's java.sql.Types defines many other types that do not appear in any of the SQL standards, but correspond to database type systems.
⁵ Decimal might be mapped to floats or doubles in a result type, but have different semantics for mathematical operations etc.
⁶ Following Mark's suggestion on the mailing list.