TRUNCATE() SQL Commands TRUNCATE()
NAME
TRUNCATE - empty a table or set of tables
SYNOPSIS
TRUNCATE [ TABLE ] name [, ...] [ CASCADE | RESTRICT ]
DESCRIPTION
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.
PARAMETERS
name The name (optionally schema-qualified) of a table to be trun-
cated.
CASCADE
Automatically truncate all tables that have foreign-key refer-
ences to any of the named tables, or to any tables added to the
group due to CASCADE.
RESTRICT
Refuse to truncate if any of the tables have foreign-key refer-
ences from tables that are not to be truncated. This is the
default.
NOTES
Only the owner of a table can TRUNCATE it.
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 run any ON DELETE triggers that might exist for the
tables.
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 ta-
ble 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 ta-
ble and other tables in the database.
TRUNCATE is transaction-safe, however: the truncation will be
safely rolled back if the surrounding transaction does not com-
mit.
EXAMPLES
Truncate the tables bigtable and fattable:
TRUNCATE bigtable, fattable;
Truncate the table othertable, and cascade to any tables that reference
othertable via foreign-key constraints:
TRUNCATE othertable CASCADE;
COMPATIBILITY
There is no TRUNCATE command in the SQL standard.
SQL - Language Statements 2008-09-19 TRUNCATE()
postgresql 8.3.4 - Generated Sun Oct 5 09:39:42 CDT 2008