<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Boolean Type</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.6.21 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Data Types" HREF="datatype.html"><LINK REL="PREVIOUS" TITLE="Date/Time Types" HREF="datatype-datetime.html"><LINK REL="NEXT" TITLE="Enumerated Types" HREF="datatype-enum.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2021-02-27T18:26:08"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="4" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.6.21 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="Date/Time Types" HREF="datatype-datetime.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="datatype.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 8. Data Types</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="Enumerated Types" HREF="datatype-enum.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><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 ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="datatype-datetime.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="datatype-enum.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Date/Time Types</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="datatype.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Enumerated Types</TD ></TR ></TABLE ></DIV ></BODY ></HTML >