Using portable data types

Only a limited set of data types are really portable across several database engines.

The ANSI SQL specification defines standard data types, but for historical reasons most databases vendors have implemented native (non-standard) data types. You can usually use a synonym for ANSI types, but the database server will uses the native types behind the scenes. For example, when you create a table with an INTEGER column in Oracle, the native NUMBER data type is used.

In your programs, avoid data types that do not have a native equivalent in the target database. This includes simple types like floating point numbers, as well as complex data types like INTERVAL. Numbers may cause rounding or overflow problems, because the values stored in the database have different limits. For the DECIMAL types, always use the same precision and scale for the program variables and the database columns.

To write portable applications, we strongly recommend using the following data types only:
  • CHAR(n)
  • VARCHAR(n)
  • BIGINT
  • INTEGER
  • SMALLINT
  • DECIMAL(p,s)
  • DATE
  • DATETIME HOUR TO MINUTE
  • DATETIME HOUR TO SECOND
  • DATETIME HOUR TO FRACTION(n)
  • DATETIME YEAR TO MINUTE
  • DATETIME YEAR TO SECOND
  • DATETIME YEAR TO FRACTION(n)
Only if the target DB engine provides an equivalent native SQL type:
  • TEXT/BYTE (for LOBs)
  • INTERVAL YEAR(p) TO MONTH
  • INTERVAL DAY(p) TO MINUTE
  • INTERVAL DAY(p) TO SECOND
  • INTERVAL DAY(p) TO FRACTION(n)
Table 1. Data type differences in database engine brands
Database Server Type Data type topic
IBM® Informix® Genero BDL is based on Informix SQL data types...
Microsoft™ SQL Server SQL types mapping: SQL Server
Oracle® MySQL / MariadDB SQL types mapping: Oracle MySQL
Oracle Database Server SQL types mapping: Oracle database
PostgreSQL SQL types mapping: PostgreSQL
SAP HANA® SQL types mapping: SAP HANA
SQLite SQL types mapping: SQLite
Dameng® SQL types mapping: Dameng