1TRUNCATE(7) PostgreSQL 9.2.24 Documentation TRUNCATE(7)
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6 TRUNCATE - empty a table or set of tables
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9 TRUNCATE [ TABLE ] [ ONLY ] name [ * ] [, ... ]
10 [ RESTART IDENTITY | CONTINUE IDENTITY ] [ CASCADE | RESTRICT ]
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13 TRUNCATE quickly removes all rows from a set of tables. It has the same
14 effect as an unqualified DELETE on each table, but since it does not
15 actually scan the tables it is faster. Furthermore, it reclaims disk
16 space immediately, rather than requiring a subsequent VACUUM operation.
17 This is most useful on large tables.
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20 name
21 The name (optionally schema-qualified) of a table to truncate. If
22 ONLY is specified before the table name, only that table is
23 truncated. If ONLY is not specified, the table and all its
24 descendant tables (if any) are truncated. Optionally, * can be
25 specified after the table name to explicitly indicate that
26 descendant tables are included.
27 RESTART IDENTITY
29 Automatically restart sequences owned by columns of the truncated
30 table(s).
31 CONTINUE IDENTITY
33 Do not change the values of sequences. This is the default.
34 CASCADE
36 Automatically truncate all tables that have foreign-key references
37 to any of the named tables, or to any tables added to the group due
38 to CASCADE.
39 RESTRICT
41 Refuse to truncate if any of the tables have foreign-key references
42 from tables that are not listed in the command. This is the
43 default.
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46 You must have the TRUNCATE privilege on a table to truncate it.
47 TRUNCATE acquires an ACCESS EXCLUSIVE lock on each table it operates
49 on, which blocks all other concurrent operations on the table. When
50 RESTART IDENTITY is specified, any sequences that are to be restarted
51 are likewise locked exclusively. If concurrent access to a table is
52 required, then the DELETE command should be used instead.
53 TRUNCATE cannot be used on a table that has foreign-key references from
55 other tables, unless all such tables are also truncated in the same
56 command. Checking validity in such cases would require table scans, and
57 the whole point is not to do one. The CASCADE option can be used to
58 automatically include all dependent tables — but be very careful when
59 using this option, or else you might lose data you did not intend to!
60 TRUNCATE will not fire any ON DELETE triggers that might exist for the
62 tables. But it will fire ON TRUNCATE triggers. If ON TRUNCATE triggers
63 are defined for any of the tables, then all BEFORE TRUNCATE triggers
64 are fired before any truncation happens, and all AFTER TRUNCATE
65 triggers are fired after the last truncation is performed and any
66 sequences are reset. The triggers will fire in the order that the
67 tables are to be processed (first those listed in the command, and then
68 any that were added due to cascading).
69 TRUNCATE is not MVCC-safe. After truncation, the table will appear
71 empty to concurrent transactions, if they are using a snapshot taken
72 before the truncation occurred. See Section 13.5, “Caveats”, in the
73 documentation for more details.
74 TRUNCATE is transaction-safe with respect to the data in the tables:
76 the truncation will be safely rolled back if the surrounding
77 transaction does not commit.
78 When RESTART IDENTITY is specified, the implied ALTER SEQUENCE RESTART
80 operations are also done transactionally; that is, they will be rolled
81 back if the surrounding transaction does not commit. This is unlike the
82 normal behavior of ALTER SEQUENCE RESTART. Be aware that if any
83 additional sequence operations are done on the restarted sequences
84 before the transaction rolls back, the effects of these operations on
85 the sequences will be rolled back, but not their effects on currval();
86 that is, after the transaction currval() will continue to reflect the
87 last sequence value obtained inside the failed transaction, even though
88 the sequence itself may no longer be consistent with that. This is
89 similar to the usual behavior of currval() after a failed transaction.
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92 Truncate the tables bigtable and fattable:
93 TRUNCATE bigtable, fattable;
95 The same, and also reset any associated sequence generators:
97 TRUNCATE bigtable, fattable RESTART IDENTITY;
99 Truncate the table othertable, and cascade to any tables that reference
101 othertable via foreign-key constraints:
102 TRUNCATE othertable CASCADE;
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106 The SQL:2008 standard includes a TRUNCATE command with the syntax
107 TRUNCATE TABLE tablename. The clauses CONTINUE IDENTITY/RESTART
108 IDENTITY also appear in that standard, but have slightly different
109 though related meanings. Some of the concurrency behavior of this
110 command is left implementation-defined by the standard, so the above
111 notes should be considered and compared with other implementations if
112 necessary.
113PostgreSQL 9.2.24 2017-11-06 TRUNCATE(7)