<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >UPDATE</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 8.3.1 Documentation" HREF="index.html"><LINK REL="UP" TITLE="SQL Commands" HREF="sql-commands.html"><LINK REL="PREVIOUS" TITLE="UNLISTEN" HREF="sql-unlisten.html"><LINK REL="NEXT" TITLE="VACUUM" HREF="sql-vacuum.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2008-03-15T03:19:10"></HEAD ><BODY CLASS="REFENTRY" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" >PostgreSQL 8.3.1 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="sql-unlisten.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="sql-unlisten.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="sql-vacuum.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="sql-vacuum.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="SQL-UPDATE" ></A >UPDATE</H1 ><DIV CLASS="REFNAMEDIV" ><A NAME="AEN60884" ></A ><H2 >Name</H2 >UPDATE -- update rows of a table</DIV ><A NAME="AEN60887" ></A ><DIV CLASS="REFSYNOPSISDIV" ><A NAME="AEN60889" ></A ><H2 >Synopsis</H2 ><PRE CLASS="SYNOPSIS" >UPDATE [ ONLY ] <TT CLASS="REPLACEABLE" ><I >table</I ></TT > [ [ AS ] <TT CLASS="REPLACEABLE" ><I >alias</I ></TT > ] SET { <TT CLASS="REPLACEABLE" ><I >column</I ></TT > = { <TT CLASS="REPLACEABLE" ><I >expression</I ></TT > | DEFAULT } | ( <TT CLASS="REPLACEABLE" ><I >column</I ></TT > [, ...] ) = ( { <TT CLASS="REPLACEABLE" ><I >expression</I ></TT > | DEFAULT } [, ...] ) } [, ...] [ FROM <TT CLASS="REPLACEABLE" ><I >fromlist</I ></TT > ] [ WHERE <TT CLASS="REPLACEABLE" ><I >condition</I ></TT > | WHERE CURRENT OF <TT CLASS="REPLACEABLE" ><I >cursor_name</I ></TT > ] [ RETURNING * | <TT CLASS="REPLACEABLE" ><I >output_expression</I ></TT > [ AS <TT CLASS="REPLACEABLE" ><I >output_name</I ></TT > ] [, ...] ]</PRE ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN60902" ></A ><H2 >Description</H2 ><P > <TT CLASS="COMMAND" >UPDATE</TT > 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 <TT CLASS="LITERAL" >SET</TT > clause; columns not explicitly modified retain their previous values. </P ><P > By default, <TT CLASS="COMMAND" >UPDATE</TT > will update rows in the specified table and all its subtables. If you wish to only update the specific table mentioned, you must use the <TT CLASS="LITERAL" >ONLY</TT > clause. </P ><P > 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 <TT CLASS="LITERAL" >FROM</TT > clause. Which technique is more appropriate depends on the specific circumstances. </P ><P > The optional <TT CLASS="LITERAL" >RETURNING</TT > clause causes <TT CLASS="COMMAND" >UPDATE</TT > 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 <TT CLASS="LITERAL" >FROM</TT >, can be computed. The new (post-update) values of the table's columns are used. The syntax of the <TT CLASS="LITERAL" >RETURNING</TT > list is identical to that of the output list of <TT CLASS="COMMAND" >SELECT</TT >. </P ><P > You must have the <TT CLASS="LITERAL" >UPDATE</TT > privilege on the table to update it, as well as the <TT CLASS="LITERAL" >SELECT</TT > privilege to any table whose values are read in the <TT CLASS="REPLACEABLE" ><I >expressions</I ></TT > or <TT CLASS="REPLACEABLE" ><I >condition</I ></TT >. </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN60923" ></A ><H2 >Parameters</H2 ><P ></P ><DIV CLASS="VARIABLELIST" ><DL ><DT ><TT CLASS="REPLACEABLE" ><I >table</I ></TT ></DT ><DD ><P > The name (optionally schema-qualified) of the table to update. </P ></DD ><DT ><TT CLASS="REPLACEABLE" ><I >alias</I ></TT ></DT ><DD ><P > A substitute name for the target table. When an alias is provided, it completely hides the actual name of the table. For example, given <TT CLASS="LITERAL" >UPDATE foo AS f</TT >, the remainder of the <TT CLASS="COMMAND" >UPDATE</TT > statement must refer to this table as <TT CLASS="LITERAL" >f</TT > not <TT CLASS="LITERAL" >foo</TT >. </P ></DD ><DT ><TT CLASS="REPLACEABLE" ><I >column</I ></TT ></DT ><DD ><P > The name of a column in <TT CLASS="REPLACEABLE" ><I >table</I ></TT >. The column name can be qualified with a subfield name or array subscript, if needed. Do not include the table's name in the specification of a target column — for example, <TT CLASS="LITERAL" >UPDATE tab SET tab.col = 1</TT > is invalid. </P ></DD ><DT ><TT CLASS="REPLACEABLE" ><I >expression</I ></TT ></DT ><DD ><P > An expression to assign to the column. The expression can use the old values of this and other columns in the table. </P ></DD ><DT ><TT CLASS="LITERAL" >DEFAULT</TT ></DT ><DD ><P > Set the column to its default value (which will be NULL if no specific default expression has been assigned to it). </P ></DD ><DT ><TT CLASS="REPLACEABLE" ><I >fromlist</I ></TT ></DT ><DD ><P > A list of table expressions, allowing columns from other tables to appear in the <TT CLASS="LITERAL" >WHERE</TT > condition and the update expressions. This is similar to the list of tables that can be specified in the <A HREF="sql-select.html#SQL-FROM" ><I ><I >FROM</I > Clause</I ></A > of a <TT CLASS="COMMAND" >SELECT</TT > statement. Note that the target table must not appear in the <TT CLASS="REPLACEABLE" ><I >fromlist</I ></TT >, unless you intend a self-join (in which case it must appear with an alias in the <TT CLASS="REPLACEABLE" ><I >fromlist</I ></TT >). </P ></DD ><DT ><TT CLASS="REPLACEABLE" ><I >condition</I ></TT ></DT ><DD ><P > An expression that returns a value of type <TT CLASS="TYPE" >boolean</TT >. Only rows for which this expression returns <TT CLASS="LITERAL" >true</TT > will be updated. </P ></DD ><DT ><TT CLASS="REPLACEABLE" ><I >cursor_name</I ></TT ></DT ><DD ><P > The name of the cursor to use in a <TT CLASS="LITERAL" >WHERE CURRENT OF</TT > condition. The row to be updated is the one most recently fetched from this cursor. The cursor must be a simple (non-join, non-aggregate) query on the <TT CLASS="COMMAND" >UPDATE</TT >'s target table. Note that <TT CLASS="LITERAL" >WHERE CURRENT OF</TT > cannot be specified together with a Boolean condition. </P ></DD ><DT ><TT CLASS="REPLACEABLE" ><I >output_expression</I ></TT ></DT ><DD ><P > An expression to be computed and returned by the <TT CLASS="COMMAND" >UPDATE</TT > command after each row is updated. The expression can use any column names of the <TT CLASS="REPLACEABLE" ><I >table</I ></TT > or table(s) listed in <TT CLASS="LITERAL" >FROM</TT >. Write <TT CLASS="LITERAL" >*</TT > to return all columns. </P ></DD ><DT ><TT CLASS="REPLACEABLE" ><I >output_name</I ></TT ></DT ><DD ><P > A name to use for a returned column. </P ></DD ></DL ></DIV ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN60996" ></A ><H2 >Outputs</H2 ><P > On successful completion, an <TT CLASS="COMMAND" >UPDATE</TT > command returns a command tag of the form </P><PRE CLASS="SCREEN" >UPDATE <TT CLASS="REPLACEABLE" ><I >count</I ></TT ></PRE ><P> The <TT CLASS="REPLACEABLE" ><I >count</I ></TT > is the number of rows updated. If <TT CLASS="REPLACEABLE" ><I >count</I ></TT > is 0, no rows matched the <TT CLASS="REPLACEABLE" ><I >condition</I ></TT > (this is not considered an error). </P ><P > If the <TT CLASS="COMMAND" >UPDATE</TT > command contains a <TT CLASS="LITERAL" >RETURNING</TT > clause, the result will be similar to that of a <TT CLASS="COMMAND" >SELECT</TT > statement containing the columns and values defined in the <TT CLASS="LITERAL" >RETURNING</TT > list, computed over the row(s) updated by the command. </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN61010" ></A ><H2 >Notes</H2 ><P > When a <TT CLASS="LITERAL" >FROM</TT > clause is present, what essentially happens is that the target table is joined to the tables mentioned in the <TT CLASS="REPLACEABLE" ><I >fromlist</I ></TT >, and each output row of the join represents an update operation for the target table. When using <TT CLASS="LITERAL" >FROM</TT > 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. </P ><P > Because of this indeterminacy, referencing other tables only within sub-selects is safer, though often harder to read and slower than using a join. </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN61017" ></A ><H2 >Examples</H2 ><P > Change the word <TT CLASS="LITERAL" >Drama</TT > to <TT CLASS="LITERAL" >Dramatic</TT > in the column <TT CLASS="STRUCTFIELD" >kind</TT > of the table <TT CLASS="STRUCTNAME" >films</TT >: </P><PRE CLASS="PROGRAMLISTING" >UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';</PRE ><P> </P ><P > Adjust temperature entries and reset precipitation to its default value in one row of the table <TT CLASS="STRUCTNAME" >weather</TT >: </P><PRE CLASS="PROGRAMLISTING" >UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT WHERE city = 'San Francisco' AND date = '2003-07-03';</PRE ><P> </P ><P > Perform the same operation and return the updated entries: </P><PRE CLASS="PROGRAMLISTING" >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;</PRE ><P> </P ><P > Use the alternative column-list syntax to do the same update: </P><PRE CLASS="PROGRAMLISTING" >UPDATE weather SET (temp_lo, temp_hi, prcp) = (temp_lo+1, temp_lo+15, DEFAULT) WHERE city = 'San Francisco' AND date = '2003-07-03';</PRE ><P> </P ><P > Increment the sales count of the salesperson who manages the account for Acme Corporation, using the <TT CLASS="LITERAL" >FROM</TT > clause syntax: </P><PRE CLASS="PROGRAMLISTING" >UPDATE employees SET sales_count = sales_count + 1 FROM accounts WHERE accounts.name = 'Acme Corporation' AND employees.id = accounts.sales_person;</PRE ><P> </P ><P > Perform the same operation, using a sub-select in the <TT CLASS="LITERAL" >WHERE</TT > clause: </P><PRE CLASS="PROGRAMLISTING" >UPDATE employees SET sales_count = sales_count + 1 WHERE id = (SELECT sales_person FROM accounts WHERE name = 'Acme Corporation');</PRE ><P> </P ><P > 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: </P><PRE CLASS="PROGRAMLISTING" >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;</PRE ><P> </P ><P > Change the <TT CLASS="STRUCTFIELD" >kind</TT > column of the table <TT CLASS="STRUCTNAME" >films</TT > in the row on which the cursor <TT CLASS="LITERAL" >c_films</TT > is currently positioned: </P><PRE CLASS="PROGRAMLISTING" >UPDATE films SET kind = 'Dramatic' WHERE CURRENT OF c_films;</PRE ><P> </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN61045" ></A ><H2 >Compatibility</H2 ><P > This command conforms to the <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > standard, except that the <TT CLASS="LITERAL" >FROM</TT > and <TT CLASS="LITERAL" >RETURNING</TT > clauses are <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > extensions. </P ><P > According to the standard, the column-list syntax should allow a list of columns to be assigned from a single row-valued expression, such as a sub-select: </P><PRE CLASS="PROGRAMLISTING" >UPDATE accounts SET (contact_last_name, contact_first_name) = (SELECT last_name, first_name FROM salesmen WHERE salesmen.id = accounts.sales_id);</PRE ><P> This is not currently implemented — the source must be a list of independent expressions. </P ><P > Some other database systems offer a <TT CLASS="LITERAL" >FROM</TT > option in which the target table is supposed to be listed again within <TT CLASS="LITERAL" >FROM</TT >. That is not how <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > interprets <TT CLASS="LITERAL" >FROM</TT >. Be careful when porting applications that use this extension. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="sql-unlisten.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="sql-vacuum.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >UNLISTEN</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="sql-commands.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >VACUUM</TD ></TR ></TABLE ></DIV ></BODY ></HTML >