Provided by: postgresql-client-8.4_8.4.11-1_i386 bug


       TRUNCATE - empty a table or set of tables


       TRUNCATE [ TABLE ] [ ONLY ] name [, ... ]


       TRUNCATE quickly removes all rows from a set of tables. It has the same
       effect as an unqualified DELETE on each table, but since  it  does  not
       actually  scan  the  tables it is faster. Furthermore, it reclaims disk
       space immediately, rather than requiring a subsequent VACUUM operation.
       This is most useful on large tables.


       name   The   name  (optionally  schema-qualified)  of  a  table  to  be
              truncated. If ONLY is specified, only that table  is  truncated.
              If  ONLY  is  not  specified,  the  table and all its descendant
              tables (if any) are truncated.

              Automatically  restart  sequences  owned  by  columns   of   the
              truncated table(s).

              Do not change the values of sequences. This is the default.

              Automatically   truncate   all   tables  that  have  foreign-key
              references to any of the named tables, or to any tables added to
              the group due to CASCADE.

              Refuse  to  truncate  if  any  of  the  tables  have foreign-key
              references from tables that are not listed in the command.  This
              is the default.


       You must have the TRUNCATE privilege on a table to truncate it.

       TRUNCATE  acquires  an  ACCESS EXCLUSIVE lock on each table it operates
       on, which blocks all other  concurrent  operations  on  the  table.  If
       concurrent  access  to  a  table  is  required, then the DELETE command
       should be used instead.

       TRUNCATE cannot be used on a table that has foreign-key references from
       other  tables,  unless  all  such tables are also truncated in the same
       command. Checking validity in such cases would require table scans, and
       the  whole  point  is  not to do one. The CASCADE option can be used to
       automatically include all dependent tables — but be very  careful  when
       using this option, or else you might lose data you did not intend to!

       TRUNCATE  will not fire any ON DELETE triggers that might exist for the
       tables. But it will fire ON TRUNCATE triggers.  If ON TRUNCATE triggers
       are  defined  for  any of the tables, then all BEFORE TRUNCATE triggers
       are fired  before  any  truncation  happens,  and  all  AFTER  TRUNCATE
       triggers are fired after the last truncation is performed. The triggers
       will fire in the order that the tables are to be processed (first those
       listed in the command, and then any that were added due to cascading).

              Warning: TRUNCATE is not MVCC-safe (see in the documentation for
              general information about MVCC).  After  truncation,  the  table
              will  appear  empty to all concurrent transactions, even if they
              are using a snapshot taken before the truncation occurred.  This
              will  only be an issue for a transaction that did not access the
              truncated table before the truncation happened — any transaction
              that has done so would hold at least an ACCESS SHARE lock, which
              would  block  TRUNCATE  until  that  transaction  completes.  So
              truncation  will  not  cause  any  apparent inconsistency in the
              table contents for successive queries on the same table, but  it
              could  cause  visible  inconsistency between the contents of the
              truncated table and other tables in the database.

       TRUNCATE is transaction-safe with respect to the data  in  the  tables:
       the   truncation   will  be  safely  rolled  back  if  the  surrounding
       transaction does not commit.

              Warning: Any ALTER SEQUENCE RESTART operations  performed  as  a
              consequence   of   using   the   RESTART   IDENTITY  option  are
              nontransactional and will not be  rolled  back  on  failure.  To
              minimize the risk, these operations are performed only after all
              the rest of TRUNCATE's work is done. However, there is  still  a
              risk if TRUNCATE is performed inside a transaction block that is
              aborted afterwards. For example, consider

              COPY foo FROM ...;

              If the COPY fails partway through, the  table  data  rolls  back
              correctly,  but  the sequences will be left with values that are
              probably smaller than  they  had  before,  possibly  leading  to
              duplicate-key  failures or other problems in later transactions.
              If this is likely to be a problem,  it's  best  to  avoid  using
              RESTART  IDENTITY, and accept that the new contents of the table
              will have higher serial numbers than the old.


       Truncate the tables bigtable and fattable:

       TRUNCATE bigtable, fattable;

       The same, and also reset any associated sequence generators:

       TRUNCATE bigtable, fattable RESTART IDENTITY;

       Truncate the table othertable, and cascade to any tables that reference
       othertable via foreign-key constraints:

       TRUNCATE othertable CASCADE;


       The  SQL:2008  standard  includes  a  TRUNCATE  command with the syntax
       TRUNCATE  TABLE  tablename.   The  clauses  CONTINUE   IDENTITY/RESTART
       IDENTITY  also  appear in that standard but have slightly different but
       related meanings.  Some of the concurrency behavior of this command  is
       left  implementation-defined by the standard, so the above notes should
       be considered and compared with other implementations if necessary.