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><H1
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><A
NAME="DATATYPE-BOOLEAN"
>8.6. Boolean Type</A
></H1
><P
>    <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> provides the
    standard <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> type <TT
CLASS="TYPE"
>boolean</TT
>;
    see <A
HREF="datatype-boolean.html#DATATYPE-BOOLEAN-TABLE"
>Table 8-19</A
>.
    The <TT
CLASS="TYPE"
>boolean</TT
> type can have several states:
    <SPAN
CLASS="QUOTE"
>"true"</SPAN
>, <SPAN
CLASS="QUOTE"
>"false"</SPAN
>, and a third state,
    <SPAN
CLASS="QUOTE"
>"unknown"</SPAN
>, which is represented by the
    <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> null value.
   </P
><DIV
CLASS="TABLE"
><A
NAME="DATATYPE-BOOLEAN-TABLE"
></A
><P
><B
>Table 8-19. Boolean Data Type</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Storage Size</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="TYPE"
>boolean</TT
></TD
><TD
>1 byte</TD
><TD
>state of true or false</TD
></TR
></TBODY
></TABLE
></DIV
><P
>    Boolean constants can be represented in SQL queries by the SQL
    key words <TT
CLASS="LITERAL"
>TRUE</TT
>, <TT
CLASS="LITERAL"
>FALSE</TT
>,
    and <TT
CLASS="LITERAL"
>NULL</TT
>.
   </P
><P
>    The datatype input function for type <TT
CLASS="TYPE"
>boolean</TT
> accepts these
    string representations for the <SPAN
CLASS="QUOTE"
>"true"</SPAN
> state:
    <P
></P
><TABLE
BORDER="0"
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
>true</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>yes</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>on</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>1</TT
></TD
></TR
></TBODY
></TABLE
><P
></P
>
    and these representations for the <SPAN
CLASS="QUOTE"
>"false"</SPAN
> state:
    <P
></P
><TABLE
BORDER="0"
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
>false</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>no</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>off</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>0</TT
></TD
></TR
></TBODY
></TABLE
><P
></P
>
    Unique prefixes of these strings are also accepted, for
    example <TT
CLASS="LITERAL"
>t</TT
> or <TT
CLASS="LITERAL"
>n</TT
>.
    Leading or trailing whitespace is ignored, and case does not matter.
   </P
><P
>    The datatype output function for type <TT
CLASS="TYPE"
>boolean</TT
> always emits
    either <TT
CLASS="LITERAL"
>t</TT
> or <TT
CLASS="LITERAL"
>f</TT
>, as shown in
    <A
HREF="datatype-boolean.html#DATATYPE-BOOLEAN-EXAMPLE"
>Example 8-2</A
>.
   </P
><DIV
CLASS="EXAMPLE"
><A
NAME="DATATYPE-BOOLEAN-EXAMPLE"
></A
><P
><B
>Example 8-2. Using the <TT
CLASS="TYPE"
>boolean</TT
> Type</B
></P
><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE test1 (a boolean, b text);
INSERT INTO test1 VALUES (TRUE, 'sic est');
INSERT INTO test1 VALUES (FALSE, 'non est');
SELECT * FROM test1;
 a |    b
---+---------
 t | sic est
 f | non est

SELECT * FROM test1 WHERE a;
 a |    b
---+---------
 t | sic est</PRE
></DIV
><P
>    The key words <TT
CLASS="LITERAL"
>TRUE</TT
> and <TT
CLASS="LITERAL"
>FALSE</TT
> are
    the preferred (<ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>-compliant) method for writing
    Boolean constants in SQL queries.  But you can also use the string
    representations by following the generic string-literal constant syntax
    described in <A
HREF="sql-syntax-lexical.html#SQL-SYNTAX-CONSTANTS-GENERIC"
>Section 4.1.2.7</A
>, for
    example <TT
CLASS="LITERAL"
>'yes'::boolean</TT
>.
   </P
><P
>    Note that the parser automatically understands
    that <TT
CLASS="LITERAL"
>TRUE</TT
> and <TT
CLASS="LITERAL"
>FALSE</TT
> are of
    type <TT
CLASS="TYPE"
>boolean</TT
>, but this is not so
    for <TT
CLASS="LITERAL"
>NULL</TT
> because that can have any type.
    So in some contexts you might have to cast <TT
CLASS="LITERAL"
>NULL</TT
>
    to <TT
CLASS="TYPE"
>boolean</TT
> explicitly, for
    example <TT
CLASS="LITERAL"
>NULL::boolean</TT
>.  Conversely, the cast can be
    omitted from a string-literal Boolean value in contexts where the parser
    can deduce that the literal must be of type <TT
CLASS="TYPE"
>boolean</TT
>.
   </P
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