Federated query information

Executing an SQL statement in a federated database requires the ability to perform portions of the statement on other data sources.

The following output from the db2expln command indicates that a data source will be read:

   Ship Distributed Subquery #n
   |   #Columns = n

If predicates are applied to data that is returned from a distributed subquery, the number of predicates being applied is indicated by the following statements:

   Residual Predicate(s)
   |   #Predicates = n

An insert, update, or delete operation that occurs at a data source is indicated by one of the following statements:

   Ship Distributed Insert #n
   Ship Distributed Update #n
   Ship Distributed Delete #n

If a table is explicitly locked at a data source, the following statement appears:

   Ship Distributed Lock Table #n

Data definition language (DDL) statements against a data source are split into two parts. The part that is invoked at the data source is indicated by the following statement:

   Ship Distributed DDL Statement #n

If the federated server is a partitioned database, part of the DDL statement must be run at the catalog database partition. This is indicated by the following statement:

   Distributed DDL Statement #n Completion

The details for each distributed sub-statement are displayed separately.

The data source for the subquery is indicated by one of the following statements:

   Server: server_name (type, version)
   Server: server_name (type)
   Server: server_name

If the data source is relational, the SQL for the sub-statement is displayed as follows:
```
   SQL Statement:
        statement
```
Non-relational data sources are indicated with:
```
   Non-Relational Data Source
```
Nicknames that are referenced in the sub-statement are listed as follows:
```
   Nicknames Referenced:
      schema.nickname ID = n
```
If the data source is relational, the base table for the nickname is displayed as follows:
```
   Base = baseschema.basetable
```
If the data source is non-relational, the source file for the nickname is displayed as follows:
```
   Source File = filename
```
If values are passed from the federated server to the data source before executing the sub-statement, the number of values is indicated by the following statement:
```
   #Input Columns: n
```
If values are passed from the data source to the federated server after executing the sub-statement, the number of values is indicated by the following statement:
```
   #Output Columns: n
```