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UPDATE

UPDATE — update rows of a table

Synopsis

[ 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 ]    [ RETURNING { * |output_expression [ [ AS ]output_name ] } [, ...] ]

Description

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 theSET 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 theFROM clause. Which technique is more appropriate depends on the specific circumstances.

The optionalRETURNING clause causesUPDATE 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 inFROM, can be computed. The new (post-update) values of the table's columns are used. The syntax of theRETURNING list is identical to that of the output list ofSELECT.

You must have theUPDATE privilege on the table, or at least on the column(s) that are listed to be updated. You must also have theSELECT privilege on any column whose values are read in theexpressions orcondition.

Parameters

Outputs

On successful completion, anUPDATE command returns a command tag of the form

UPDATEcount

Thecount 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 thecondition when updates were suppressed by aBEFORE UPDATE trigger. Ifcount is 0, no rows were updated by the query (this is not considered an error).

If theUPDATE command contains aRETURNING clause, the result will be similar to that of aSELECT statement containing the columns and values defined in theRETURNING list, computed over the row(s) updated by the command.

Notes

When aFROM clause is present, what essentially happens is that the target table is joined to the tables mentioned in thefrom_item list, and each output row of the join represents an update operation for the target table. When usingFROM 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 aDELETE andINSERT operation.

There is a possibility that a concurrentUPDATE orDELETE on the row being moved will get a serialization failure error. Suppose session 1 is performing anUPDATE on a partition key, and meanwhile a concurrent session 2 for which this row is visible performs anUPDATE orDELETE operation on this row. In such case, session 2'sUPDATE orDELETE 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 theUPDATE/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.

An attempt of moving a row from one partition to another will fail if a foreign key is found to directly reference an ancestor of the source partition that is not the same as the ancestor that's mentioned in theUPDATE query.

Examples

Change the wordDrama toDramatic in the columnkind of the tablefilms:

UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';

Adjust temperature entries and reset precipitation to its default value in one row of the tableweather:

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 theFROM 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 theWHERE 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 salespeople:

UPDATE accounts SET (contact_first_name, contact_last_name) =    (SELECT first_name, last_name FROM employees     WHERE employees.id = accounts.sales_person);

A similar result could be accomplished with a join:

UPDATE accounts SET contact_first_name = first_name,                    contact_last_name = last_name  FROM employees WHERE employees.id = accounts.sales_person;

However, the second query may give unexpected results ifemployees.id is not a unique key, whereas the first query is guaranteed to raise an error if there are multipleid matches. Also, if there is no match for a particularaccounts.sales_person 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 operationsSAVEPOINT 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 eventuallyCOMMIT;

Change thekind column of the tablefilms in the row on which the cursorc_films is currently positioned:

UPDATE films SET kind = 'Dramatic' WHERE CURRENT OF c_films;

Updates affecting many rows can have negative effects on system performance, such as table bloat, increased replica lag, and increased lock contention. In such situations it can make sense to perform the operation in smaller batches, possibly with aVACUUM operation on the table between batches. While there is noLIMIT clause forUPDATE, it is possible to get a similar effect through the use of aCommon Table Expression and a self-join. With the standardPostgres Pro table access method, a self-join on the system columnctid is very efficient:

WITH exceeded_max_retries AS (  SELECT w.ctid FROM work_item AS w    WHERE w.status = 'active' AND w.num_retries > 10    ORDER BY w.retry_timestamp    FOR UPDATE    LIMIT 5000)UPDATE work_item SET status = 'failed'  FROM exceeded_max_retries AS emr  WHERE work_item.ctid = emr.ctid;

This command will need to be repeated until no rows remain to be updated. Use of anORDER BY clause allows the command to prioritize which rows will be updated; it can also prevent deadlock with other update operations if they use the same ordering. If lock contention is a concern, thenSKIP LOCKED can be added to theCTE to prevent multiple commands from updating the same row. However, then a finalUPDATE withoutSKIP LOCKED orLIMIT will be needed to ensure that no matching rows were overlooked.

Compatibility

This command conforms to theSQL standard, except that theFROM andRETURNING clauses arePostgres Pro extensions, as is the ability to useWITH withUPDATE.

Some other database systems offer aFROM option in which the target table is supposed to be listed again withinFROM. That is not howPostgres Pro interpretsFROM. 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.Postgres Pro only allows the source value to be arow constructor or a sub-SELECT. An individual column's updated value can be specified asDEFAULT in the row-constructor case, but not inside a sub-SELECT.