diff options
Diffstat (limited to '')
| -rw-r--r-- | doc/src/sgml/man7/UPDATE.7 | 473 |
1 files changed, 473 insertions, 0 deletions
diff --git a/doc/src/sgml/man7/UPDATE.7 b/doc/src/sgml/man7/UPDATE.7 new file mode 100644 index 0000000..2ea895b --- /dev/null +++ b/doc/src/sgml/man7/UPDATE.7 @@ -0,0 +1,473 @@ +'\" t +.\" Title: UPDATE +.\" Author: The PostgreSQL Global Development Group +.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/> +.\" Date: 2024 +.\" Manual: PostgreSQL 16.2 Documentation +.\" Source: PostgreSQL 16.2 +.\" Language: English +.\" +.TH "UPDATE" "7" "2024" "PostgreSQL 16.2" "PostgreSQL 16.2 Documentation" +.\" ----------------------------------------------------------------- +.\" * Define some portability stuff +.\" ----------------------------------------------------------------- +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" http://bugs.debian.org/507673 +.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.ie \n(.g .ds Aq \(aq +.el .ds Aq ' +.\" ----------------------------------------------------------------- +.\" * set default formatting +.\" ----------------------------------------------------------------- +.\" disable hyphenation +.nh +.\" disable justification (adjust text to left margin only) +.ad l +.\" ----------------------------------------------------------------- +.\" * MAIN CONTENT STARTS HERE * +.\" ----------------------------------------------------------------- +.SH "NAME" +UPDATE \- update rows of a table +.SH "SYNOPSIS" +.sp +.nf +[ WITH [ RECURSIVE ] \fIwith_query\fR [, \&.\&.\&.] ] +UPDATE [ ONLY ] \fItable_name\fR [ * ] [ [ AS ] \fIalias\fR ] + SET { \fIcolumn_name\fR = { \fIexpression\fR | DEFAULT } | + ( \fIcolumn_name\fR [, \&.\&.\&.] ) = [ ROW ] ( { \fIexpression\fR | DEFAULT } [, \&.\&.\&.] ) | + ( \fIcolumn_name\fR [, \&.\&.\&.] ) = ( \fIsub\-SELECT\fR ) + } [, \&.\&.\&.] + [ FROM \fIfrom_item\fR [, \&.\&.\&.] ] + [ WHERE \fIcondition\fR | WHERE CURRENT OF \fIcursor_name\fR ] + [ RETURNING * | \fIoutput_expression\fR [ [ AS ] \fIoutput_name\fR ] [, \&.\&.\&.] ] +.fi +.SH "DESCRIPTION" +.PP +\fBUPDATE\fR +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\&. +.PP +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\&. +.PP +The optional +RETURNING +clause causes +\fBUPDATE\fR +to compute and return value(s) based on each row actually updated\&. Any expression using the table\*(Aqs columns, and/or columns of other tables mentioned in +FROM, can be computed\&. The new (post\-update) values of the table\*(Aqs columns are used\&. The syntax of the +RETURNING +list is identical to that of the output list of +\fBSELECT\fR\&. +.PP +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 +\fIexpressions\fR +or +\fIcondition\fR\&. +.SH "PARAMETERS" +.PP +\fIwith_query\fR +.RS 4 +The +WITH +clause allows you to specify one or more subqueries that can be referenced by name in the +\fBUPDATE\fR +query\&. See +Section\ \&7.8 +and +\fBSELECT\fR(7) +for details\&. +.RE +.PP +\fItable_name\fR +.RS 4 +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\&. +.RE +.PP +\fIalias\fR +.RS 4 +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 +\fBUPDATE\fR +statement must refer to this table as +f +not +foo\&. +.RE +.PP +\fIcolumn_name\fR +.RS 4 +The name of a column in the table named by +\fItable_name\fR\&. The column name can be qualified with a subfield name or array subscript, if needed\&. Do not include the table\*(Aqs name in the specification of a target column \(em for example, +UPDATE table_name SET table_name\&.col = 1 +is invalid\&. +.RE +.PP +\fIexpression\fR +.RS 4 +An expression to assign to the column\&. The expression can use the old values of this and other columns in the table\&. +.RE +.PP +DEFAULT +.RS 4 +Set the column to its default value (which will be NULL if no specific default expression has been assigned to it)\&. 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\&. +.RE +.PP +\fIsub\-SELECT\fR +.RS 4 +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\&. +.RE +.PP +\fIfrom_item\fR +.RS 4 +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 +\fBSELECT\fR +statement; for example, an alias for the table name can be specified\&. Do not repeat the target table as a +\fIfrom_item\fR +unless you intend a self\-join (in which case it must appear with an alias in the +\fIfrom_item\fR)\&. +.RE +.PP +\fIcondition\fR +.RS 4 +An expression that returns a value of type +boolean\&. Only rows for which this expression returns +true +will be updated\&. +.RE +.PP +\fIcursor_name\fR +.RS 4 +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 +\fBUPDATE\fR\*(Aqs target table\&. Note that +WHERE CURRENT OF +cannot be specified together with a Boolean condition\&. See +\fBDECLARE\fR(7) +for more information about using cursors with +WHERE CURRENT OF\&. +.RE +.PP +\fIoutput_expression\fR +.RS 4 +An expression to be computed and returned by the +\fBUPDATE\fR +command after each row is updated\&. The expression can use any column names of the table named by +\fItable_name\fR +or table(s) listed in +FROM\&. Write +* +to return all columns\&. +.RE +.PP +\fIoutput_name\fR +.RS 4 +A name to use for a returned column\&. +.RE +.SH "OUTPUTS" +.PP +On successful completion, an +\fBUPDATE\fR +command returns a command tag of the form +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE \fIcount\fR +.fi +.if n \{\ +.RE +.\} +.sp +The +\fIcount\fR +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 +\fIcondition\fR +when updates were suppressed by a +BEFORE UPDATE +trigger\&. If +\fIcount\fR +is 0, no rows were updated by the query (this is not considered an error)\&. +.PP +If the +\fBUPDATE\fR +command contains a +RETURNING +clause, the result will be similar to that of a +\fBSELECT\fR +statement containing the columns and values defined in the +RETURNING +list, computed over the row(s) updated by the command\&. +.SH "NOTES" +.PP +When a +FROM +clause is present, what essentially happens is that the target table is joined to the tables mentioned in the +\fIfrom_item\fR +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\*(Aqt 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\&. +.PP +Because of this indeterminacy, referencing other tables only within sub\-selects is safer, though often harder to read and slower than using a join\&. +.PP +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 +\fBDELETE\fR +and +\fBINSERT\fR +operation\&. +.PP +There is a possibility that a concurrent +\fBUPDATE\fR +or +\fBDELETE\fR +on the row being moved will get a serialization failure error\&. Suppose session 1 is performing an +\fBUPDATE\fR +on a partition key, and meanwhile a concurrent session 2 for which this row is visible performs an +\fBUPDATE\fR +or +\fBDELETE\fR +operation on this row\&. In such case, session 2\*(Aqs +\fBUPDATE\fR +or +\fBDELETE\fR +will detect the row movement and raise a serialization failure error (which always returns with an SQLSTATE code \*(Aq40001\*(Aq)\&. 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 +\fBUPDATE\fR/\fBDELETE\fR +on this new row version\&. +.PP +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\&. +.PP +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\*(Aqs mentioned in the +\fBUPDATE\fR +query\&. +.SH "EXAMPLES" +.PP +Change the word +Drama +to +Dramatic +in the column +kind +of the table +films: +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE films SET kind = \*(AqDramatic\*(Aq WHERE kind = \*(AqDrama\*(Aq; +.fi +.if n \{\ +.RE +.\} +.PP +Adjust temperature entries and reset precipitation to its default value in one row of the table +weather: +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT + WHERE city = \*(AqSan Francisco\*(Aq AND date = \*(Aq2003\-07\-03\*(Aq; +.fi +.if n \{\ +.RE +.\} +.PP +Perform the same operation and return the updated entries: +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT + WHERE city = \*(AqSan Francisco\*(Aq AND date = \*(Aq2003\-07\-03\*(Aq + RETURNING temp_lo, temp_hi, prcp; +.fi +.if n \{\ +.RE +.\} +.PP +Use the alternative column\-list syntax to do the same update: +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE weather SET (temp_lo, temp_hi, prcp) = (temp_lo+1, temp_lo+15, DEFAULT) + WHERE city = \*(AqSan Francisco\*(Aq AND date = \*(Aq2003\-07\-03\*(Aq; +.fi +.if n \{\ +.RE +.\} +.PP +Increment the sales count of the salesperson who manages the account for Acme Corporation, using the +FROM +clause syntax: +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE employees SET sales_count = sales_count + 1 FROM accounts + WHERE accounts\&.name = \*(AqAcme Corporation\*(Aq + AND employees\&.id = accounts\&.sales_person; +.fi +.if n \{\ +.RE +.\} +.PP +Perform the same operation, using a sub\-select in the +WHERE +clause: +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE employees SET sales_count = sales_count + 1 WHERE id = + (SELECT sales_person FROM accounts WHERE name = \*(AqAcme Corporation\*(Aq); +.fi +.if n \{\ +.RE +.\} +.PP +Update contact names in an accounts table to match the currently assigned salespeople: +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE accounts SET (contact_first_name, contact_last_name) = + (SELECT first_name, last_name FROM employees + WHERE employees\&.id = accounts\&.sales_person); +.fi +.if n \{\ +.RE +.\} +.sp +A similar result could be accomplished with a join: +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE accounts SET contact_first_name = first_name, + contact_last_name = last_name + FROM employees WHERE employees\&.id = accounts\&.sales_person; +.fi +.if n \{\ +.RE +.\} +.sp +However, the second query may give unexpected results if +employees\&.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_person +entry, the first query will set the corresponding name fields to NULL, whereas the second query will not update that row at all\&. +.PP +Update statistics in a summary table to match the current data: +.sp +.if n \{\ +.RS 4 +.\} +.nf +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); +.fi +.if n \{\ +.RE +.\} +.PP +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: +.sp +.if n \{\ +.RS 4 +.\} +.nf +BEGIN; +\-\- other operations +SAVEPOINT sp1; +INSERT INTO wines VALUES(\*(AqChateau Lafite 2003\*(Aq, \*(Aq24\*(Aq); +\-\- 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 = \*(AqChateau Lafite 2003\*(Aq; +\-\- continue with other operations, and eventually +COMMIT; +.fi +.if n \{\ +.RE +.\} +.PP +Change the +kind +column of the table +films +in the row on which the cursor +c_films +is currently positioned: +.sp +.if n \{\ +.RS 4 +.\} +.nf +UPDATE films SET kind = \*(AqDramatic\*(Aq WHERE CURRENT OF c_films; +.fi +.if n \{\ +.RE +.\} +.SH "COMPATIBILITY" +.PP +This command conforms to the +SQL +standard, except that the +FROM +and +RETURNING +clauses are +PostgreSQL +extensions, as is the ability to use +WITH +with +\fBUPDATE\fR\&. +.PP +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 +PostgreSQL +interprets +FROM\&. Be careful when porting applications that use this extension\&. +.PP +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\&. +PostgreSQL +only allows the source value to be a +row constructor +or a sub\-SELECT\&. An individual column\*(Aqs updated value can be specified as +DEFAULT +in the row\-constructor case, but not inside a sub\-SELECT\&. |