Tables
The following restrictions exist for tables:
• Ingres RDBMS coerces different column types.
• All host DBMSs do not allow a union between result tables that may have different underlying column types.
• DB2 UDB column names in union select statements
With the DB2 UDB gateway, the column name for the union select statement is the column number in the select list for any column where any column names in the select list do not match. This behavior differs from Ingres. For Ingres, the column name for union selects is the name of the column for the first select in the union select statement. For example, the following statement:
select mgr from gwemp union select name from gwemp
yields a column name of mgr for Ingres, whereas the DB2 UDB gateway yields a column name of 1.
• In Microsoft SQL Server, tables, views, and indexes used through the gateway cannot start with the prefix SYS.