Understanding Data Type Differences

There are a number of differences between the Java programming language data types and SQL Server 2005 data types. The Microsoft SQL Server 2005 JDBC Driver helps to facilitate those differences through various types of conversions.

Character Types

The JDBC character string data types are CHAR, VARCHAR, and LONGVARCHAR.

Type Description

Fixed-length

The SQL Server char and nchar data types map directly to the JDBC CHAR type. These are fixed-length types with padding provided by the server in the case where the column has SET ANSI_PADDING ON. Padding is always turned on for nchar, but for char, in the case where the server char columns are not padded, the JDBC driver adds the padding.

Variable-length

The SQL Server varchar and nvarchar types map directly to the JDBC VARCHAR type.

Long

The SQL Server text and ntext types map to the JDBC LONGVARCHAR type. These are deprecated types for SQL Server 2005, so you should use large value types instead.

Using the update<Numeric Type> and updateObject (int, java.lang.Object) methods will fail against text and ntext server columns. However, using the setObject method with a specified character conversion type is supported against text and ntext server columns.

Binary String Types

The JDBC binary-string types are BINARY, VARBINARY, and LONGVARBINARY.

Type Description

Fixed-length

The SQL Server binary type maps directly to the JDBC BINARY type. This is a fixed-length type with padding provided by the server in the case where the column has SET ANSI_PADDING ON. When the server char columns are not padded, the JDBC driver adds the padding.

The SQL Server timestamp type is a JDBC BINARY type with the fixed length of 8 bytes.

Variable-length

The SQL Server varbinary type maps to the JDBC VARBINARY type.

Long

The SQL Server image type maps to the JDBC LONGVARBINARY type. This type is deprecated for SQL Server 2005, so you should use a large value type instead.

The udt type in SQL Server 2005 maps to JDBC as a LONGBINARY type.

Exact Numeric Types

The JDBC exact numeric types map directly to their corresponding SQL Server types.

Type Description

BIT

The JDBC BIT type represents a single bit that can be 0 or 1. This maps to a SQL Server bit type.

TINYINT

The JDBC TINYINT type represents a single byte. This maps to a SQL Server tinyint type.

SMALLINT

The JDBC SMALLINT type represents a signed 16-bit integer. This maps to a SQL Server smallint type.

INTEGER

The JDBC INTEGER type represents a signed 32-bit integer. This maps to a SQL Server int type.

BIGINT

The JDBC BIGINT type represents a signed 64-bit integer. This maps to a SQL Server bigint type.

NUMERIC

The JDBC NUMERIC type represents a fixed-precision decimal value that holds values of identical precision. The NUMERIC type maps to the SQL Server numeric type.

DECIMAL

The JDBC DECIMAL type represents a fixed-precision decimal value that holds values of at least the specified precision. The DECIMAL type maps to the SQL Server decimal type.

The JDBC DECIMAL type also maps to the SQL Server money and smallmoney types, which are specific fixed-precision decimal types that are stored in 8 and 4 bytes, respectively.

Approximate Numeric Types

The JDBC approximate numeric types are REAL, DOUBLE, and FLOAT.

Type Description

REAL

The JDBC REAL type has seven digits of precision (single precision) and maps directly to the SQL Server real type.

DOUBLE

The JDBC DOUBLE type has 15 digits of precision (double precision) and maps to the SQL Server float type. The JDBC FLOAT type is a synonym of DOUBLE. Because there can be confusion between FLOAT and DOUBLE, DOUBLE is preferred.

Datetime Types

The JDBC TIMESTAMP type maps to the SQL Server datetime and smalldatetime types. The datetime type is stored in two 4-byte integers. The smalldatetime type holds the same information (date and time), but with less accuracy, in two 2-byte small integers.

NoteNote:

The SQL Server timestamp type is a fixed-length binary-string type. It does not map to any of the JDBC time types: DATE, TIME, or TIMESTAMP.

Custom Type Mapping

The custom type mapping feature of JDBC that uses the SQLData interfaces for the JDBC advanced types (UDTs, Struct, and so on). is not implemented in the JDBC driver.

See Also

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