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func.sgml has grown over the years to the point where it is very difficult to manage. This commit splits out each sect1 piece into its own file, which is then included in the main file, so that the built documentation should be identical to the pre-split documentation. All these new files are placed in a new "func" subdirectory, and the previous func.sgml is removed. Done using scripts developed by: Author: jian he <jian.universality@gmail.com> Discussion: https://postgr.es/m/CACJufxFgAh1--EMwOjMuANe=VTmjkNaZjH+AzSe04-8ZCGiESA@mail.gmail.com
147 lines
3.5 KiB
Plaintext
147 lines
3.5 KiB
Plaintext
<sect1 id="functions-logical">
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<title>Logical Operators</title>
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<indexterm zone="functions-logical">
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<primary>operator</primary>
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<secondary>logical</secondary>
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</indexterm>
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<indexterm>
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<primary>Boolean</primary>
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<secondary>operators</secondary>
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<see>operators, logical</see>
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</indexterm>
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<para>
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The usual logical operators are available:
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<indexterm>
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<primary>AND (operator)</primary>
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</indexterm>
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<indexterm>
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<primary>OR (operator)</primary>
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</indexterm>
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<indexterm>
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<primary>NOT (operator)</primary>
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</indexterm>
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<indexterm>
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<primary>conjunction</primary>
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</indexterm>
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<indexterm>
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<primary>disjunction</primary>
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</indexterm>
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<indexterm>
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<primary>negation</primary>
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</indexterm>
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<synopsis>
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<type>boolean</type> <literal>AND</literal> <type>boolean</type> <returnvalue>boolean</returnvalue>
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<type>boolean</type> <literal>OR</literal> <type>boolean</type> <returnvalue>boolean</returnvalue>
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<literal>NOT</literal> <type>boolean</type> <returnvalue>boolean</returnvalue>
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</synopsis>
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<acronym>SQL</acronym> uses a three-valued logic system with true,
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false, and <literal>null</literal>, which represents <quote>unknown</quote>.
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Observe the following truth tables:
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<informaltable>
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<tgroup cols="4">
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<thead>
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<row>
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<entry><replaceable>a</replaceable></entry>
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<entry><replaceable>b</replaceable></entry>
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<entry><replaceable>a</replaceable> AND <replaceable>b</replaceable></entry>
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<entry><replaceable>a</replaceable> OR <replaceable>b</replaceable></entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>TRUE</entry>
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<entry>TRUE</entry>
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<entry>TRUE</entry>
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<entry>TRUE</entry>
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</row>
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<row>
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<entry>TRUE</entry>
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<entry>FALSE</entry>
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<entry>FALSE</entry>
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<entry>TRUE</entry>
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</row>
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<row>
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<entry>TRUE</entry>
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<entry>NULL</entry>
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<entry>NULL</entry>
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<entry>TRUE</entry>
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</row>
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<row>
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<entry>FALSE</entry>
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<entry>FALSE</entry>
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<entry>FALSE</entry>
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<entry>FALSE</entry>
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</row>
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<row>
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<entry>FALSE</entry>
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<entry>NULL</entry>
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<entry>FALSE</entry>
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<entry>NULL</entry>
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</row>
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<row>
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<entry>NULL</entry>
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<entry>NULL</entry>
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<entry>NULL</entry>
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<entry>NULL</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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<informaltable>
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<tgroup cols="2">
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<thead>
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<row>
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<entry><replaceable>a</replaceable></entry>
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<entry>NOT <replaceable>a</replaceable></entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>TRUE</entry>
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<entry>FALSE</entry>
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</row>
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<row>
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<entry>FALSE</entry>
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<entry>TRUE</entry>
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</row>
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<row>
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<entry>NULL</entry>
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<entry>NULL</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</para>
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<para>
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The operators <literal>AND</literal> and <literal>OR</literal> are
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commutative, that is, you can switch the left and right operands
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without affecting the result. (However, it is not guaranteed that
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the left operand is evaluated before the right operand. See <xref
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linkend="syntax-express-eval"/> for more information about the
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order of evaluation of subexpressions.)
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</para>
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</sect1>
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