UPDATE — update rows of a table
[ WITH [ RECURSIVE ]with_query
[, ...] ] UPDATE [ ONLY ]table_name
[ * ] [ [ AS ]alias
] SET {column_name
= {expression
| DEFAULT } | (column_name
[, ...] ) = [ ROW ] ( {expression
| DEFAULT } [, ...] ) | (column_name
[, ...] ) = (sub-SELECT
) } [, ...] [ FROMfrom_item
[, ...] ] [ WHEREcondition
| WHERE CURRENT OFcursor_name
] [ ORDER BYexpression
[ ASC | DESC | USINGoperator
] [ NULLS { FIRST | LAST } ] [, ...] ] [ LIMIT {count
| ALL } ] [ OFFSETstart
[ ROW | ROWS ] ] [ RETURNING * |output_expression
[ [ AS ]output_name
] [, ...] ]
UPDATE
changes the values of the specified
columns in all rows that satisfy the condition. Only the columns to
be modified need be mentioned in the SET
clause;
columns not explicitly modified retain their previous values.
There are two ways to modify a table using information contained in
other tables in the database: using sub-selects, or specifying
additional tables in the FROM
clause. Which
technique is more appropriate depends on the specific
circumstances.
The optional RETURNING
clause causes UPDATE
to compute and return value(s) based on each row actually updated.
Any expression using the table's columns, and/or columns of other
tables mentioned in FROM
, can be computed.
The new (post-update) values of the table's columns are used.
The syntax of the RETURNING
list is identical to that of the
output list of SELECT
.
You must have the UPDATE
privilege on the table,
or at least on the column(s) that are listed to be updated.
You must also have the SELECT
privilege on any column whose values are read in the
expressions
or
condition
.
If the ORDER BY
clause is specified, you can update rows in the specified order.
It's semantic like SELECT
ORDER BY
clause. Notice, do not support
update inherit table with ORDER BY
clause, not support canopy also.
If the LIMIT
or OFFSET
clause is specified, you can update a subset of rows. It's semantic like SELECT
LIMIT
clause. Notice, do not support update inherit table with LIMIT
or OFFSET
clause, not support canopy also.
with_query
The WITH
clause allows you to specify one or more
subqueries that can be referenced by name in the UPDATE
query. See Section 7.8 and SELECT
for details.
table_name
The name (optionally schema-qualified) of the table to update.
If ONLY
is specified before the table name, matching rows
are updated in the named table only. If ONLY
is not
specified, matching rows are also updated in any tables inheriting from
the named table. Optionally, *
can be specified after the
table name to explicitly indicate that descendant tables are included.
alias
A substitute name for the target table. When an alias is
provided, it completely hides the actual name of the table. For
example, given UPDATE foo AS f
, the remainder of the
UPDATE
statement must refer to this table as
f
not foo
.
column_name
The name of a column in the table named by table_name
.
The column name can be qualified with a subfield name or array
subscript, if needed. It can also use alias to qualify name.
for example,
UPDATE table_name AS t SET t.col = 1
.
Do not include the table's name in the
specification of a target column — for example,
UPDATE table_name SET table_name.col = 1
is invalid.
expression
An expression to assign to the column. The expression can use the old values of this and other columns in the table.
DEFAULT
Set the column to its default value (which will be NULL if no specific default expression has been assigned to it). If the expression references other columns, DEFAULT is not allowed. An identity column will be set to a new value generated by the associated sequence. For a generated column, specifying this is permitted but merely specifies the normal behavior of computing the column from its generation expression.
sub-SELECT
A SELECT
sub-query that produces as many output columns
as are listed in the parenthesized column list preceding it. The
sub-query must yield no more than one row when executed. If it
yields one row, its column values are assigned to the target columns;
if it yields no rows, NULL values are assigned to the target columns.
The sub-query can refer to old values of the current row of the table
being updated.
from_item
A table expression allowing columns from other tables to appear in
the WHERE
condition and update expressions. This
uses the same syntax as the FROM
clause of
a SELECT
statement;
for example, an alias for the table name can be specified. Do not
repeat the target table as a from_item
unless you intend a self-join (in which case it must appear with
an alias in the from_item
).
condition
An expression that returns a value of type boolean
.
Only rows for which this expression returns true
will be updated.
cursor_name
The name of the cursor to use in a WHERE CURRENT OF
condition. The row to be updated is the one most recently fetched
from this cursor. The cursor must be a non-grouping
query on the UPDATE
's target table.
Note that WHERE CURRENT OF
cannot be
specified together with a Boolean condition. See
DECLARE
for more information about using cursors with
WHERE CURRENT OF
.
output_expression
An expression to be computed and returned by the UPDATE
command after each row is updated. The expression can use any
column names of the table named by table_name
or table(s) listed in FROM
.
Write *
to return all columns.
output_name
A name to use for a returned column.
On successful completion, an UPDATE
command returns a command
tag of the form
UPDATE count
The count
is the number
of rows updated, including matched rows whose values did not change.
Note that the number may be less than the number of rows that matched
the condition
when
updates were suppressed by a BEFORE UPDATE
trigger. If
count
is 0, no rows were
updated by the query (this is not considered an error).
If the UPDATE
command contains a RETURNING
clause, the result will be similar to that of a SELECT
statement containing the columns and values defined in the
RETURNING
list, computed over the row(s) updated by the
command.
When a FROM
clause is present, what essentially happens
is that the target table is joined to the tables mentioned in the
from_item
list, and each output row of the join
represents an update operation for the target table. When using
FROM
you should ensure that the join
produces at most one output row for each row to be modified. In
other words, a target row shouldn't join to more than one row from
the other table(s). If it does, then only one of the join rows
will be used to update the target row, but which one will be used
is not readily predictable.
Because of this indeterminacy, referencing other tables only within sub-selects is safer, though often harder to read and slower than using a join.
In the case of a partitioned table, updating a row might cause it to no
longer satisfy the partition constraint of the containing partition. In that
case, if there is some other partition in the partition tree for which this
row satisfies its partition constraint, then the row is moved to that
partition. If there is no such partition, an error will occur. Behind the
scenes, the row movement is actually a DELETE
and
INSERT
operation.
There is a possibility that a concurrent UPDATE
or
DELETE
on the row being moved will get a serialization
failure error. Suppose session 1 is performing an UPDATE
on a partition key, and meanwhile a concurrent session 2 for which this
row is visible performs an UPDATE
or
DELETE
operation on this row. In such case,
session 2's UPDATE
or DELETE
will
detect the row movement and raise a serialization failure error (which
always returns with an SQLSTATE code '40001'). Applications may wish to
retry the transaction if this occurs. In the usual case where the table
is not partitioned, or where there is no row movement, session 2 would
have identified the newly updated row and carried out the
UPDATE
/DELETE
on this new row
version.
Note that while rows can be moved from local partitions to a foreign-table partition (provided the foreign data wrapper supports tuple routing), they cannot be moved from a foreign-table partition to another partition.
Change the word Drama
to Dramatic
in the
column kind
of the table films
:
UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';
Adjust temperature entries and reset precipitation to its default
value in one row of the table weather
:
UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT WHERE city = 'San Francisco' AND date = '2003-07-03';
Perform the same operation and return the updated entries:
UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT WHERE city = 'San Francisco' AND date = '2003-07-03' RETURNING temp_lo, temp_hi, prcp;
Use the alternative column-list syntax to do the same update:
UPDATE weather SET (temp_lo, temp_hi, prcp) = (temp_lo+1, temp_lo+15, DEFAULT) WHERE city = 'San Francisco' AND date = '2003-07-03';
Increment the sales count of the salesperson who manages the
account for Acme Corporation, using the FROM
clause syntax:
UPDATE employees SET sales_count = sales_count + 1 FROM accounts WHERE accounts.name = 'Acme Corporation' AND employees.id = accounts.sales_person;
Perform the same operation, using a sub-select in the
WHERE
clause:
UPDATE employees SET sales_count = sales_count + 1 WHERE id = (SELECT sales_person FROM accounts WHERE name = 'Acme Corporation');
Update contact names in an accounts table to match the currently assigned salesmen:
UPDATE accounts SET (contact_first_name, contact_last_name) = (SELECT first_name, last_name FROM salesmen WHERE salesmen.id = accounts.sales_id);
A similar result could be accomplished with a join:
UPDATE accounts SET contact_first_name = first_name, contact_last_name = last_name FROM salesmen WHERE salesmen.id = accounts.sales_id;
However, the second query may give unexpected results
if salesmen
.id
is not a unique key, whereas
the first query is guaranteed to raise an error if there are multiple
id
matches. Also, if there is no match for a particular
accounts
.sales_id
entry, the first query
will set the corresponding name fields to NULL, whereas the second query
will not update that row at all.
Update statistics in a summary table to match the current data:
UPDATE summary s SET (sum_x, sum_y, avg_x, avg_y) = (SELECT sum(x), sum(y), avg(x), avg(y) FROM data d WHERE d.group_id = s.group_id);
Attempt to insert a new stock item along with the quantity of stock. If the item already exists, instead update the stock count of the existing item. To do this without failing the entire transaction, use savepoints:
BEGIN; -- other operations SAVEPOINT sp1; INSERT INTO wines VALUES('Chateau Lafite 2003', '24'); -- Assume the above fails because of a unique key violation, -- so now we issue these commands: ROLLBACK TO sp1; UPDATE wines SET stock = stock + 24 WHERE winename = 'Chateau Lafite 2003'; -- continue with other operations, and eventually COMMIT;
Change the kind
column of the table
films
in the row on which the cursor
c_films
is currently positioned:
UPDATE films SET kind = 'Dramatic' WHERE CURRENT OF c_films;
Change the name
column of table citys
order by id
limit 5 .
UPDATE citys SET name = 'null' order by id LIMIT 5;
This command conforms to the SQL standard, except
that the FROM
and RETURNING
clauses
are LightDB extensions, as is the ability
to use WITH
with UPDATE
.
Some other database systems offer a FROM
option in which
the target table is supposed to be listed again within FROM
.
That is not how LightDB interprets
FROM
. Be careful when porting applications that use this
extension.
According to the standard, the source value for a parenthesized sub-list of
target column names can be any row-valued expression yielding the correct
number of columns. LightDB only allows the
source value to be a row
constructor or a sub-SELECT
. An individual column's
updated value can be specified as DEFAULT
in the
row-constructor case, but not inside a sub-SELECT
.