Firebird 2.1 Language Reference Update

DML statements
Description: A SELECT query used in an INSERT statement may now be a UNION.
Example:
insert into Members (number, name)
select number, name from NewMembers where Accepted = 1
union
select number, name from SuspendedMembers where Vindicated = 1
Available in: DSQL, PSQL
Added in: 2.1
MERGE
Description: Merges data into a table or view. The source may a table, view or derived table (i.e. a parenthesized
SELECT statement or CTE). Each source record will be used to update one or more target records, insert a new
record in the target table, or neither. The action taken depends on the provided condition and the WHEN clause(s).
The condition will typically contain a comparison of fields in the source and target relations.
Syntax:
MERGE INTO {tablename | viewname} [[AS] alias]
USING {tablename | viewname | (select_stmt)} [[AS] alias]
ON condition
WHEN MATCHED THEN UPDATE SET colname = value [, colname = value ...]
WHEN NOT MATCHED THEN INSERT [()] VALUES ()
::= colname [, colname ...]
::= value [, value ...]
Examples:
Note: It is allowed to provide only one of the WHEN clauses
merge into books b
using purchases p
on p.title = b.title and p.type = 'bk'
when matched then
update set b.desc = b.desc || '; ' || p.desc
when not matched then
insert (title, desc, bought) values (p.title, p.desc, p.bought)
merge into customers c
using (select * from customers_delta where id > 10) cd
on (c.id = cd.id)
when matched then update set name = cd.name
when not matched then insert (id, name) values (cd.id, cd.name)
Note
WHEN NOT MATCHED should be interpreted from the point of view of the source (the relation in the USING
clause). That is: if a source record doesn't have a match in the target table, the INSERT clause is executed.
Conversely, records in the target table without a matching source record don't trigger any action.
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