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><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
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><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN216163"
></A
><P
><B
>例 1. max_length aggregation function example</B
></P
><TABLE
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><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
>
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