DataTypeMapper element
If the JDBC driver does not provide a generic SQL data type for a column or the JDBC driver provides an incorrect data type, use the DataTypeMapper element in mappings.xml to map the column’s database data type to a generic SQL data type. The DataTypeMapper element has one child element, DataTypes. The DataTypes element has one child element, DataType.
For each database data type you want to map, you define a DataType element. You should declare all VARCHAR and DECIMAL (or NUMERIC) data types using the DataType element. If these data types are not declared, the Integration service uses the ODBC escape sequences to convert these types. The escape sequences cannot specify the string length, decimal precision, or decimal scale of the result.
Each DataType element has the attributes shown in Table 10-2.
Maximum size (decimal precision or string length) for the database data type. Applies only to CHAR, VARCHAR, LONGVARCHAR, NUMERIC, and DECIMAL types.
No, but highly recommended.

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