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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Running SQL Commands</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 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="ECPG - Embedded SQL in C" HREF="ecpg.html"><LINK REL="PREVIOUS" TITLE="Managing Database Connections" HREF="ecpg-connect.html"><LINK REL="NEXT" TITLE="Using Host Variables" HREF="ecpg-variables.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="2017-11-06T22:43:11"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="Managing Database Connections" HREF="ecpg-connect.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="ecpg.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 33. <SPAN CLASS="APPLICATION" >ECPG</SPAN > - Embedded <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > in C</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="Using Host Variables" HREF="ecpg-variables.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="ECPG-COMMANDS" >33.3. Running SQL Commands</A ></H1 ><P > Any SQL command can be run from within an embedded SQL application. Below are some examples of how to do that. </P ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="ECPG-EXECUTING" >33.3.1. Executing SQL Statements</A ></H2 ><P > Creating a table: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL CREATE TABLE foo (number integer, ascii char(16)); EXEC SQL CREATE UNIQUE INDEX num1 ON foo(number); EXEC SQL COMMIT;</PRE ><P> </P ><P > Inserting rows: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL INSERT INTO foo (number, ascii) VALUES (9999, 'doodad'); EXEC SQL COMMIT;</PRE ><P> </P ><P > Deleting rows: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL DELETE FROM foo WHERE number = 9999; EXEC SQL COMMIT;</PRE ><P> </P ><P > Updates: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL UPDATE foo SET ascii = 'foobar' WHERE number = 9999; EXEC SQL COMMIT;</PRE ><P> </P ><P > <TT CLASS="LITERAL" >SELECT</TT > statements that return a single result row can also be executed using <TT CLASS="LITERAL" >EXEC SQL</TT > directly. To handle result sets with multiple rows, an application has to use a cursor; see <A HREF="ecpg-commands.html#ECPG-CURSORS" >Section 33.3.2</A > below. (As a special case, an application can fetch multiple rows at once into an array host variable; see <A HREF="ecpg-variables.html#ECPG-VARIABLES-ARRAYS" >Section 33.4.4.3.1</A >.) </P ><P > Single-row select: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL SELECT foo INTO :FooBar FROM table1 WHERE ascii = 'doodad';</PRE ><P> </P ><P > Also, a configuration parameter can be retrieved with the <TT CLASS="LITERAL" >SHOW</TT > command: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL SHOW search_path INTO :var;</PRE ><P> </P ><P > The tokens of the form <TT CLASS="LITERAL" >:<TT CLASS="REPLACEABLE" ><I >something</I ></TT ></TT > are <I CLASS="FIRSTTERM" >host variables</I >, that is, they refer to variables in the C program. They are explained in <A HREF="ecpg-variables.html" >Section 33.4</A >. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="ECPG-CURSORS" >33.3.2. Using Cursors</A ></H2 ><P > To retrieve a result set holding multiple rows, an application has to declare a cursor and fetch each row from the cursor. The steps to use a cursor are the following: declare a cursor, open it, fetch a row from the cursor, repeat, and finally close it. </P ><P > Select using cursors: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL DECLARE foo_bar CURSOR FOR SELECT number, ascii FROM foo ORDER BY ascii; EXEC SQL OPEN foo_bar; EXEC SQL FETCH foo_bar INTO :FooBar, DooDad; ... EXEC SQL CLOSE foo_bar; EXEC SQL COMMIT;</PRE ><P> </P ><P > For more details about declaration of the cursor, see <A HREF="ecpg-sql-declare.html" >DECLARE</A >, and see <A HREF="sql-fetch.html" >FETCH</A > for <TT CLASS="LITERAL" >FETCH</TT > command details. </P ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > The ECPG <TT CLASS="COMMAND" >DECLARE</TT > command does not actually cause a statement to be sent to the PostgreSQL backend. The cursor is opened in the backend (using the backend's <TT CLASS="COMMAND" >DECLARE</TT > command) at the point when the <TT CLASS="COMMAND" >OPEN</TT > command is executed. </P ></BLOCKQUOTE ></DIV ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="ECPG-TRANSACTIONS" >33.3.3. Managing Transactions</A ></H2 ><P > In the default mode, statements are committed only when <TT CLASS="COMMAND" >EXEC SQL COMMIT</TT > is issued. The embedded SQL interface also supports autocommit of transactions (similar to <SPAN CLASS="APPLICATION" >libpq</SPAN > behavior) via the <TT CLASS="OPTION" >-t</TT > command-line option to <TT CLASS="COMMAND" >ecpg</TT > (see <A HREF="app-ecpg.html" ><SPAN CLASS="APPLICATION" >ecpg</SPAN ></A >) or via the <TT CLASS="LITERAL" >EXEC SQL SET AUTOCOMMIT TO ON</TT > statement. In autocommit mode, each command is automatically committed unless it is inside an explicit transaction block. This mode can be explicitly turned off using <TT CLASS="LITERAL" >EXEC SQL SET AUTOCOMMIT TO OFF</TT >. </P ><P > The following transaction management commands are available: <P ></P ></P><DIV CLASS="VARIABLELIST" ><DL ><DT ><TT CLASS="LITERAL" >EXEC SQL COMMIT</TT ></DT ><DD ><P > Commit an in-progress transaction. </P ></DD ><DT ><TT CLASS="LITERAL" >EXEC SQL ROLLBACK</TT ></DT ><DD ><P > Roll back an in-progress transaction. </P ></DD ><DT ><TT CLASS="LITERAL" >EXEC SQL SET AUTOCOMMIT TO ON</TT ></DT ><DD ><P > Enable autocommit mode. </P ></DD ><DT ><TT CLASS="LITERAL" >SET AUTOCOMMIT TO OFF</TT ></DT ><DD ><P > Disable autocommit mode. This is the default. </P ></DD ></DL ></DIV ><P> </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="ECPG-PREPARED" >33.3.4. Prepared Statements</A ></H2 ><P > When the values to be passed to an SQL statement are not known at compile time, or the same statement is going to be used many times, then prepared statements can be useful. </P ><P > The statement is prepared using the command <TT CLASS="LITERAL" >PREPARE</TT >. For the values that are not known yet, use the placeholder <SPAN CLASS="QUOTE" >"<TT CLASS="LITERAL" >?</TT >"</SPAN >: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL PREPARE stmt1 FROM "SELECT oid, datname FROM pg_database WHERE oid = ?";</PRE ><P> </P ><P > If a statement returns a single row, the application can call <TT CLASS="LITERAL" >EXECUTE</TT > after <TT CLASS="LITERAL" >PREPARE</TT > to execute the statement, supplying the actual values for the placeholders with a <TT CLASS="LITERAL" >USING</TT > clause: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL EXECUTE stmt1 INTO :dboid, :dbname USING 1;</PRE ><P> </P ><P > If a statement returns multiple rows, the application can use a cursor declared based on the prepared statement. To bind input parameters, the cursor must be opened with a <TT CLASS="LITERAL" >USING</TT > clause: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL PREPARE stmt1 FROM "SELECT oid,datname FROM pg_database WHERE oid > ?"; EXEC SQL DECLARE foo_bar CURSOR FOR stmt1; /* when end of result set reached, break out of while loop */ EXEC SQL WHENEVER NOT FOUND DO BREAK; EXEC SQL OPEN foo_bar USING 100; ... while (1) { EXEC SQL FETCH NEXT FROM foo_bar INTO :dboid, :dbname; ... } EXEC SQL CLOSE foo_bar;</PRE ><P> </P ><P > When you don't need the prepared statement anymore, you should deallocate it: </P><PRE CLASS="PROGRAMLISTING" >EXEC SQL DEALLOCATE PREPARE <TT CLASS="REPLACEABLE" ><I >name</I ></TT >;</PRE ><P> </P ><P > For more details about <TT CLASS="LITERAL" >PREPARE</TT >, see <A HREF="ecpg-sql-prepare.html" >PREPARE</A >. Also see <A HREF="ecpg-dynamic.html" >Section 33.5</A > for more details about using placeholders and input parameters. </P ></DIV ></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="ecpg-connect.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="ecpg-variables.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Managing Database Connections</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ecpg.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Using Host Variables</TD ></TR ></TABLE ></DIV ></BODY ></HTML >