<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >sqlite_create_aggregate</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="PHP 手册" HREF="index.html"><LINK REL="UP" TITLE="SQLite Functions" HREF="ref.sqlite.html"><LINK REL="PREVIOUS" TITLE="sqlite_column" HREF="function.sqlite-column.html"><LINK REL="NEXT" TITLE="sqlite_create_function" HREF="function.sqlite-create-function.html"><META HTTP-EQUIV="Content-type" CONTENT="text/html; charset=UTF-8"></HEAD ><BODY CLASS="refentry" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >PHP 手册</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="function.sqlite-column.html" ACCESSKEY="P" >上一页</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="function.sqlite-create-function.html" ACCESSKEY="N" >下一页</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="function.sqlite-create-aggregate" ></A >sqlite_create_aggregate</H1 ><DIV CLASS="refnamediv" ><A NAME="AEN216076" ></A ><P > (PHP 5)</P >sqlite_create_aggregate<P > (no version information, might be only in CVS)</P >SQLiteDatabase->createAggregate -- Register an aggregating UDF for use in SQL statements</DIV ><DIV CLASS="refsect1" ><A NAME="AEN216080" ></A ><H2 >说明</H2 >void <B CLASS="methodname" >sqlite_create_aggregate</B > ( resource dbhandle, string function_name, callback step_func, callback finalize_func [, int num_args] )<BR ></BR ><P >Object oriented style (method):</P >class <B CLASS="classname" >SQLiteDatabase</B > { <BR ></BR >void <B CLASS="methodname" >createAggregate</B > ( string function_name, callback step_func, callback finalize_func [, int num_args] )<BR ></BR >}<P > <B CLASS="function" >sqlite_create_aggregate()</B > is similar to <A HREF="function.sqlite-create-function.html" ><B CLASS="function" >sqlite_create_function()</B ></A > except that it registers functions that can be used to calculate a result aggregated across all the rows of a query. </P ><P > The key difference between this function and <A HREF="function.sqlite-create-function.html" ><B CLASS="function" >sqlite_create_function()</B ></A > is that two functions are required to manage the aggregate; <CODE CLASS="parameter" >step_func</CODE > is called for each row of the result set. Your PHP function should accumulate the result and store it into the aggregation context. Once all the rows have been processed, <CODE CLASS="parameter" >finalize_func</CODE > will be called and it should then take the data from the aggregation context and return the result. Callback functions should return a type understood by SQLite (i.e. <A HREF="language.types.html#language.types.intro" >scalar type</A >). </P ></DIV ><DIV CLASS="refsect1" ><A NAME="AEN216127" ></A ><H2 >参数</H2 ><P > <P ></P ><DIV CLASS="variablelist" ><DL ><DT ><CODE CLASS="parameter" >dbhandle</CODE ></DT ><DD ><P > The SQLite Database resource; returned from <A HREF="function.sqlite-open.html" ><B CLASS="function" >sqlite_open()</B ></A > when used procedurally. This parameter is not required when using the object-oriented method. </P ></DD ><DT ><CODE CLASS="parameter" >function_name</CODE ></DT ><DD ><P > The name of the function used in SQL statements. </P ></DD ><DT ><CODE CLASS="parameter" >step_func</CODE ></DT ><DD ><P > Callback function called for each row of the result set. </P ></DD ><DT ><CODE CLASS="parameter" >finalize_func</CODE ></DT ><DD ><P > Callback function to aggregate the "stepped" data from each row. </P ></DD ><DT ><CODE CLASS="parameter" >num_args</CODE ></DT ><DD ><P > Hint to the SQLite parser if the callback function accepts a predetermined number of arguments. </P ></DD ></DL ></DIV > </P ></DIV ><DIV CLASS="refsect1" ><A NAME="AEN216157" ></A ><H2 >返回值</H2 ><P > 无返回值。 </P ></DIV ><DIV CLASS="refsect1" ><A NAME="AEN216160" ></A ><H2 >范例</H2 ><P > <TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" CLASS="EXAMPLE" ><TR ><TD ><DIV CLASS="example" ><A NAME="AEN216163" ></A ><P ><B >例 1. max_length aggregation function example</B ></P ><TABLE BORDER="0" BGCOLOR="#E0E0E0" CELLPADDING="5" ><TR ><TD ><code><font color="#000000"> <font color="#0000BB"><?php<br />$data </font><font color="#007700">= array(<br /> </font><font color="#DD0000">'one'</font><font color="#007700">,<br /> </font><font color="#DD0000">'two'</font><font color="#007700">,<br /> </font><font color="#DD0000">'three'</font><font color="#007700">,<br /> </font><font color="#DD0000">'four'</font><font color="#007700">,<br /> </font><font color="#DD0000">'five'</font><font color="#007700">,<br /> </font><font color="#DD0000">'six'</font><font color="#007700">,<br /> </font><font color="#DD0000">'seven'</font><font color="#007700">,<br /> </font><font color="#DD0000">'eight'</font><font color="#007700">,<br /> </font><font color="#DD0000">'nine'</font><font color="#007700">,<br /> </font><font color="#DD0000">'ten'</font><font color="#007700">,<br /> );<br /></font><font color="#0000BB">$dbhandle </font><font color="#007700">= </font><font color="#0000BB">sqlite_open</font><font color="#007700">(</font><font color="#DD0000">':memory:'</font><font color="#007700">);<br /></font><font color="#0000BB">sqlite_query</font><font color="#007700">(</font><font color="#0000BB">$dbhandle</font><font color="#007700">, </font><font color="#DD0000">"CREATE TABLE strings(a)"</font><font color="#007700">);<br />foreach (</font><font color="#0000BB">$data </font><font color="#007700">as </font><font color="#0000BB">$str</font><font color="#007700">) {<br /> </font><font color="#0000BB">$str </font><font color="#007700">= </font><font color="#0000BB">sqlite_escape_string</font><font color="#007700">(</font><font color="#0000BB">$str</font><font color="#007700">);<br /> </font><font color="#0000BB">sqlite_query</font><font color="#007700">(</font><font color="#0000BB">$dbhandle</font><font color="#007700">, </font><font color="#DD0000">"INSERT INTO strings VALUES ('$str')"</font><font color="#007700">);<br />}<br /><br />function </font><font color="#0000BB">max_len_step</font><font color="#007700">(&</font><font color="#0000BB">$context</font><font color="#007700">, </font><font color="#0000BB">$string</font><font color="#007700">) <br />{<br /> if (</font><font color="#0000BB">strlen</font><font color="#007700">(</font><font color="#0000BB">$string</font><font color="#007700">) > </font><font color="#0000BB">$context</font><font color="#007700">) {<br /> </font><font color="#0000BB">$context </font><font color="#007700">= </font><font color="#0000BB">strlen</font><font color="#007700">(</font><font color="#0000BB">$string</font><font color="#007700">);<br /> }<br />}<br /><br />function </font><font color="#0000BB">max_len_finalize</font><font color="#007700">(&</font><font color="#0000BB">$context</font><font color="#007700">) <br />{<br /> return </font><font color="#0000BB">$context</font><font color="#007700">;<br />}<br /><br /></font><font color="#0000BB">sqlite_create_aggregate</font><font color="#007700">(</font><font color="#0000BB">$dbhandle</font><font color="#007700">, </font><font color="#DD0000">'max_len'</font><font color="#007700">, </font><font color="#DD0000">'max_len_step'</font><font color="#007700">, </font><font color="#DD0000">'max_len_finalize'</font><font color="#007700">);<br /><br /></font><font color="#0000BB">var_dump</font><font color="#007700">(</font><font color="#0000BB">sqlite_array_query</font><font color="#007700">(</font><font color="#0000BB">$dbhandle</font><font color="#007700">, </font><font color="#DD0000">'SELECT max_len(a) from strings'</font><font color="#007700">));<br /><br /></font><font color="#0000BB">?></font> </font> </code></TD ></TR ></TABLE ></DIV ></TD ></TR ></TABLE > </P ><P > In this example, we are creating an aggregating function that will calculate the length of the longest string in one of the columns of the table. For each row, the <TT CLASS="literal" >max_len_step</TT > function is called and passed a <CODE CLASS="parameter" >context</CODE > parameter. The context parameter is just like any other PHP variable and be set to hold an array or even an object value. In this example, we are simply using it to hold the maximum length we have seen so far; if the <CODE CLASS="parameter" >string</CODE > has a length longer than the current maximum, we update the context to hold this new maximum length. </P ><P > After all of the rows have been processed, SQLite calls the <TT CLASS="literal" >max_len_finalize</TT > function to determine the aggregate result. Here, we could perform some kind of calculation based on the data found in the <CODE CLASS="parameter" >context</CODE >. In our simple example though, we have been calculating the result as the query progressed, so we simply need to return the context value. </P ><DIV CLASS="note" ><BLOCKQUOTE CLASS="note" ><P ><B >注意: </B > The example above will not work correctly if the column contains binary data. Take a look at the manual page for <A HREF="function.sqlite-udf-decode-binary.html" ><B CLASS="function" >sqlite_udf_decode_binary()</B ></A > for an explanation of why this is so, and an example of how to make it respect the binary encoding. </P ></BLOCKQUOTE ></DIV ><DIV CLASS="tip" ><BLOCKQUOTE CLASS="tip" ><P ><B >提示: </B > It is NOT recommended for you to store a copy of the values in the context and then process them at the end, as you would cause SQLite to use a lot of memory to process the query - just think of how much memory you would need if a million rows were stored in memory, each containing a string 32 bytes in length. </P ></BLOCKQUOTE ></DIV ><DIV CLASS="tip" ><BLOCKQUOTE CLASS="tip" ><P ><B >提示: </B > You can use <A HREF="function.sqlite-create-function.html" ><B CLASS="function" >sqlite_create_function()</B ></A > and <B CLASS="function" >sqlite_create_aggregate()</B > to override SQLite native SQL functions. </P ></BLOCKQUOTE ></DIV ></DIV ><DIV CLASS="refsect1" ><A NAME="AEN216182" ></A ><H2 >参见</H2 ><P > <P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD ><A HREF="function.sqlite-create-function.html" ><B CLASS="function" >sqlite_create_function()</B ></A ></TD ></TR ><TR ><TD ><A HREF="function.sqlite-udf-encode-binary.html" ><B CLASS="function" >sqlite_udf_encode_binary()</B ></A ></TD ></TR ><TR ><TD ><A HREF="function.sqlite-udf-decode-binary.html" ><B CLASS="function" >sqlite_udf_decode_binary()</B ></A ></TD ></TR ></TBODY ></TABLE ><P ></P > </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="function.sqlite-column.html" ACCESSKEY="P" >上一页</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >起始页</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="function.sqlite-create-function.html" ACCESSKEY="N" >下一页</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >sqlite_column</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ref.sqlite.html" ACCESSKEY="U" >上一级</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >sqlite_create_function</TD ></TR ></TABLE ></DIV ></BODY ></HTML >