mirror/postgresql
2
0
Fork 0
mirror of https://git.postgresql.org/git/postgresql.git synced 2025-03-13 19:57:53 +08:00
Code Issues Packages Projects Releases Wiki Activity

Explain CHECK constraint handling in postgres_fdw's IMPORT FOREIGN SCHEMA.

Browse Source 
The existing documentation could easily be misinterpreted, and it failed to
explain the inconsistent-evaluation hazard that deterred us from supporting
automatic importing of check constraints.  Revise it.

Etsuro Fujita, further expanded by me
This commit is contained in:
Tom Lane 2015-05-25 14:12:51 -04:00
parent cdbdc43827
commit e70ec8230a
1 changed files with 12 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
doc/src/sgml/postgres-fdw.sgml
View File

@ -309,8 +309,8 @@
using <xref linkend="sql-importforeignschema">. This command creates
foreign table definitions on the local server that match tables or
views present on the remote server. If the remote tables to be imported
have columns of user-defined data types, the local server must have types
of the same names.
have columns of user-defined data types, the local server must have
compatible types of the same names.
</para>
<para>
@ -361,9 +361,16 @@
<para>
Note that constraints other than <literal>NOT NULL</> will never be
imported from the remote tables, since <productname>PostgreSQL</>
does not support any other type of constraint on a foreign table.
Checking other types of constraints is always left to the remote server.
imported from the remote tables. Although <productname>PostgreSQL</>
does support <literal>CHECK</> constraints on foreign tables, there is no
provision for importing them automatically, because of the risk that a
constraint expression could evaluate differently on the local and remote
servers. Any such inconsistency in the behavior of a <literal>CHECK</>
constraint could lead to hard-to-detect errors in query optimization.
So if you wish to import <literal>CHECK</> constraints, you must do so
manually, and you should verify the semantics of each one carefully.
For more detail about the treatment of <literal>CHECK</> constraints on
foreign tables, see <xref linkend="sql-createforeigntable">.
</para>
</sect3>
</sect2>