HELP COLUMN with a FROM Clause
If a HELP COLUMN statement contains a FROM clause, you can reference one or more tables and join indexes in the same statement if each column name is fully qualified (that is, preceded by the table name in the form tablename.columnname).
This does not apply when the referenced object is a data table name or an error table name.
HELP COLUMN for a Data Table or Error Table
If you use either the FROM ERROR TABLE FOR data_table_name syntax or the example for the FROM error_table_name syntax, then the information returned is for the column you specify in the error table associated with data_table_name, not from the base table specified by data_table_name.
The HELP COLUMN information and attributes reported by either of these syntaxes is identical to that returned by the other HELP COLUMN syntaxes, only for an error table rather than for a base data table.
See CREATE ERROR TABLE Usage Notes for more information about error tables.
Also see HELP ERROR TABLE Usage Notes.
HELP COLUMN and Indexes
If the column for which information is requested defines a single-column index, then that is reported with the uniqueness and type of index. HELP COLUMN returns index information for single-column indexes only. For multiple-column indexes, the columns are reported as not being used in an index.
HELP COLUMN does not provide information about whether a column is used in the partitioning expression of a partitioned primary index. Use SHOW TABLE (see SHOW object Usage Notes) or the system view DBC.IndexConstraintsV (see X Views for further information) to get the partitioning information.
All HELP return columns are subject to formatting using the rules described for their Export Width specification in Field Mode.
All CHAR and VARCHAR fields are affected, although the effects on VARCHAR in Record mode may not be noticeable.
HELP COLUMN and Column-Partitioned NoPI Tables and Join Indexes
Use HELP COLUMN requests to get partitioning information for a table or join index. You can also find information about indexes by using the system views DBC.Indices[V][X] and the data dictionary table DBC.Indexes.