Big-Data-HPC-Platform/docs/ECLLanguageReference/ECLR_mods/BltInFunc-KEYPATCH.xml

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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<sect1 id="KEYPATCH">
  <title>KEYPATCH</title>

  <para><emphasis>[ </emphasis><emphasis>attrname</emphasis><emphasis
  role="bold"> </emphasis><emphasis role="bold">:= ] KEYPATCH<indexterm>
      <primary>KEYPATCH</primary>
    </indexterm><indexterm>
      <primary>KEYPATCH function</primary>
    </indexterm>(</emphasis><emphasis> index, patchfile, newfile
  </emphasis><emphasis role="bold"> [, OVERWRITE<indexterm>
      <primary>OVERWRITE</primary>
    </indexterm> ] [</emphasis><emphasis>,</emphasis><emphasis role="bold">
  EXPIRE<indexterm>
      <primary>EXPIRE</primary>
    </indexterm>( [ </emphasis><emphasis>days </emphasis><emphasis
  role="bold">] ) ] );</emphasis></para>

  <informaltable colsep="1" frame="all" rowsep="1">
    <tgroup cols="2">
      <colspec colwidth="88.80pt" />

      <colspec />

      <tbody>
        <row>
          <entry><emphasis>attrname</emphasis></entry>

          <entry>Optional. The action name, which turns the action into an
          attribute definition, therefore not executed until the attrname is
          used as an action.</entry>
        </row>

        <row>
          <entry><emphasis>index</emphasis></entry>

          <entry>The INDEX attribute to apply the changes to.</entry>
        </row>

        <row>
          <entry><emphasis>patchfile</emphasis></entry>

          <entry>A string constant specifying the logical name of the file
          containing the changes to implement (created by KEYDIFF).</entry>
        </row>

        <row>
          <entry><emphasis>newfile</emphasis></entry>

          <entry>A string constant specifying the logical name of the file to
          write the new index to.</entry>
        </row>

        <row>
          <entry><emphasis role="bold">OVERWRITE</emphasis></entry>

          <entry>Optional. Specifies overwriting the
          <emphasis>newfile</emphasis> if it already exists.</entry>
        </row>

        <row>
          <entry><emphasis role="bold">EXPIRE</emphasis></entry>

          <entry>Optional. Specifies the <emphasis>newfile</emphasis> is a
          temporary file that may be automatically deleted after the specified
          number of days.</entry>
        </row>

        <row>
          <entry><emphasis>days</emphasis></entry>

          <entry>Optional. The number of days after which the file may be
          automatically deleted. If omitted, the default is seven (7).</entry>
        </row>
      </tbody>
    </tgroup>
  </informaltable>

  <para>The <emphasis role="bold">KEYPATCH </emphasis>action uses the
  <emphasis>index</emphasis> and <emphasis>patchfile</emphasis> to write a new
  index to the specified <emphasis>newfile</emphasis> containing all the
  original index data updated by the information from the
  <emphasis>patchfile</emphasis>.</para>

  <para>Example:</para>

  <programlisting>Vehicles := DATASET('vehicles',
     {STRING2 st,
      STRING20 city,
      STRING20 lname,
      UNSIGNED8 filepos{virtual(fileposition)}},
     FLAT);
i1 := INDEX(Vehicles,
  {st,city,lname,filepos},
  'vkey::20041201::st.city.lname');
i2 := INDEX(Vehicles,
  {st,city,lname,filepos},
  'vkey::20050101::st.city.lname');
a := KEYDIFF(i1,i2,'KEY::DIFF::20050101::i1i2',OVERWRITE);
b := KEYPATCH(i1,
    'KEY::DIFF::20050101::i1i2',
    'vkey::st.city.lname'OVERWRITE);    
SEQUENTIAL(a,b);
</programlisting>

  <para>See Also: <link linkend="KEYDIFF">KEYDIFF</link>, <link
  linkend="INDEX_record_structure">INDEX</link></para>
</sect1>