Big-Data-HPC-Platform/docs/ECLR_mods/Expr-LogicalOperators.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<sect1 id="Logical_Operators">
  <title>Logical Operators</title>

  <para><emphasis>The following </emphasis>logical operators<indexterm>
      <primary>logical operators</primary>
    </indexterm> are supported, listed here in their evaluation
  precedence:</para>

  <informaltable colsep="0" frame="none" rowsep="0">
    <tgroup align="left" cols="2">
      <colspec colwidth="94.80pt" />

      <colspec />

      <tbody>
        <row>
          <entry>NOT</entry>

          <entry>Boolean NOT<indexterm>
              <primary>Boolean NOT</primary>
            </indexterm> operation</entry>
        </row>

        <row>
          <entry>~</entry>

          <entry>Boolean NOT<indexterm>
              <primary>Boolean NOT</primary>
            </indexterm> operation</entry>
        </row>

        <row>
          <entry>AND</entry>

          <entry>Boolean AND<indexterm>
              <primary>Boolean AND</primary>
            </indexterm> operation</entry>
        </row>

        <row>
          <entry>OR</entry>

          <entry>Boolean OR<indexterm>
              <primary>Boolean OR</primary>
            </indexterm> operation</entry>
        </row>
      </tbody>
    </tgroup>
  </informaltable>

  <para></para>

  <sect2 id="Logical_Expression_Grouping">
    <title>Logical Expression Grouping</title>

    <para>When a complex logical expression has multiple OR conditions, you
    should group the OR conditions and order them from least complex to most
    complex to result in the most efficient processing. If the probability of
    occurrence is known, you should order them from the most likely to occur
    to the least likely to occur, because once any part of a compound OR
    condition evaluates to TRUE, the remainder of the expression is bypassed.
    This is also true of the order of MAP function conditions.</para>

    <para>Whenever AND and OR logical operations are mixed in the same
    expression, you should use parentheses to group within the expression to
    ensure correct evaluation and to clarify the intent of the expression. For
    example consider the following:</para>

    <programlisting>isCurrentRevolv := trades.trd_type = 'R' AND
                   trades.trd_rate = '0' OR
                   trades.trd_rate = '1';</programlisting>

    <para>does not produce the intended result. Use of parentheses ensures
    correct evaluation, as shown below:</para>

    <programlisting>isCurrentRevolv := trades.trd_type = 'R' AND
          (trades.trd_rate = '0' OR trades.trd_rate = '1');</programlisting>
  </sect2>

  <sect2 id="An_XOR_Operator">
    <title>An XOR Operator<indexterm>
        <primary>XOR Operator</primary>
      </indexterm></title>

    <para>The following function can be used to perform an XOR operation on 2
    Boolean values:</para>

    <programlisting>BOOLEAN XOR(BOOLEAN cond1, BOOLEAN cond2) :=
          (cond1 OR cond2) AND NOT (cond1 AND cond2);</programlisting>
  </sect2>
</sect1>