docs/build/plain-html/topics/impala_identifiers.html - impala - Git at Google

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   <h1 class="title topictitle1" id="ariaid-title1">Overview of Impala Identifiers</h1>


   <div class="body conbody">

     <p class="p">
       Identifiers are the names of databases, tables, or columns that you specify in a SQL statement. The rules for
       identifiers govern what names you can give to things you create, the notation for referring to names
       containing unusual characters, and other aspects such as case sensitivity.
     </p>


     <ul class="ul">
       <li class="li">
         <p class="p">
         The minimum length of an identifier is 1 character.
         </p>

       </li>


       <li class="li">
         <p class="p">
         The maximum length of an identifier is currently 128 characters except for column names which
         can contain 767 characters, enforced by the metastore database.
         </p>

       </li>


       <li class="li">
         <p class="p">
         An identifier must start with an alphanumeric or underscore character except for column names which
         can start with any unicode characters. Quoting the identifier with backticks has no effect on the allowed
         characters in the name.
         </p>

       </li>


       <li class="li">
         <p class="p">
         An identifier can contain only ASCII characters except for column names which can contain unicode characters.
         </p>

       </li>


       <li class="li">
         <p class="p">
         To use an identifier name that matches one of the Impala reserved keywords (listed in
         <a class="xref" href="impala_reserved_words.html#reserved_words">Impala Reserved Words</a>), surround the identifier with <code class="ph codeph">``</code>
         characters (backticks). Quote the reserved word even if it is part of a fully qualified name.
         The following example shows how a reserved word can be used as a column name if it is quoted
         with backticks in the <code class="ph codeph">CREATE TABLE</code> statement, and how the column name
         must also be quoted with backticks in a query:
         </p>

 <pre class="pre codeblock"><code>[localhost:21000] &gt; create table reserved (`data` string);

 [localhost:21000] &gt; select data from reserved;
 ERROR: AnalysisException: Syntax error in line 1:
 select data from reserved
        ^
 Encountered: DATA
 Expected: ALL, CASE, CAST, DISTINCT, EXISTS, FALSE, IF, INTERVAL, NOT, NULL, STRAIGHT_JOIN, TRUE, IDENTIFIER
 CAUSED BY: Exception: Syntax error

 [localhost:21000] &gt; select reserved.data from reserved;
 ERROR: AnalysisException: Syntax error in line 1:
 select reserved.data from reserved
                 ^
 Encountered: DATA
 Expected: IDENTIFIER
 CAUSED BY: Exception: Syntax error

 [localhost:21000] &gt; select reserved.`data` from reserved;

 [localhost:21000] &gt;
 </code></pre>

         <div class="note important"><span class="importanttitle">Important:</span>
           Because the list of reserved words grows over time as new SQL syntax is added,
           consider adopting coding conventions (especially for any automated scripts
           or in packaged applications) to always quote all identifiers with backticks.
           Quoting all identifiers protects your SQL from compatibility issues if
           new reserved words are added in later releases.
         </div>


       </li>


       <li class="li">
         <p class="p">
         Impala identifiers are always case-insensitive. That is, tables named <code class="ph codeph">t1</code> and
         <code class="ph codeph">T1</code> always refer to the same table, regardless of quote characters. Internally, Impala
         always folds all specified table and column names to lowercase. This is why the column headers in query
         output are always displayed in lowercase.
         </p>

       </li>

     </ul>


     <p class="p">
       See <a class="xref" href="impala_aliases.html#aliases">Overview of Impala Aliases</a> for how to define shorter or easier-to-remember aliases if the
       original names are long or cryptic identifiers.
       <span class="ph"> Aliases follow the same rules as identifiers when it
         comes to case insensitivity. Aliases can be longer than identifiers (up to the maximum
         length of a Java string) and can include additional characters such as spaces and dashes
         when they are quoted using backtick characters. </span>
     </p>


     <p class="p">
         Another way to define different names for the same tables or columns is to create views.
         See <a class="xref" href="../shared/../topics/impala_views.html#views">Overview of Impala Views</a> for details.
       </p>

   </div>

 <div class="related-links">
 <div class="familylinks">
 <div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_schema_objects.html">Impala Schema Objects and Object Names</a></div>
 </div>
 </div></body>
 </html>
	<?xml version="1.0" encoding="UTF-8"?>
	<!DOCTYPE html
	PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
	<head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />

	<meta name="copyright" content="(C) Copyright 2024" />
	<meta name="DC.rights.owner" content="(C) Copyright 2024" />
	<meta name="DC.Type" content="concept" />
	<meta name="DC.Title" content="Overview of Impala Identifiers" />
	<meta name="DC.Relation" scheme="URI" content="../topics/impala_schema_objects.html" />
	<meta name="prodname" content="Impala" />
	<meta name="prodname" content="Impala" />
	<meta name="version" content="Impala 3.4.x" />
	<meta name="version" content="Impala 3.4.x" />
	<meta name="DC.Format" content="XHTML" />
	<meta name="DC.Identifier" content="identifiers" />
	<link rel="stylesheet" type="text/css" href="../commonltr.css" />
	<title>Overview of Impala Identifiers</title>
	</head>
	<body id="identifiers">


	<h1 class="title topictitle1" id="ariaid-title1">Overview of Impala Identifiers</h1>




	<div class="body conbody">

	<p class="p">
	Identifiers are the names of databases, tables, or columns that you specify in a SQL statement. The rules for
	identifiers govern what names you can give to things you create, the notation for referring to names
	containing unusual characters, and other aspects such as case sensitivity.
	</p>


	<ul class="ul">
	<li class="li">
	<p class="p">
	The minimum length of an identifier is 1 character.
	</p>

	</li>


	<li class="li">
	<p class="p">
	The maximum length of an identifier is currently 128 characters except for column names which
	can contain 767 characters, enforced by the metastore database.
	</p>

	</li>


	<li class="li">
	<p class="p">
	An identifier must start with an alphanumeric or underscore character except for column names which
	can start with any unicode characters. Quoting the identifier with backticks has no effect on the allowed
	characters in the name.
	</p>

	</li>


	<li class="li">
	<p class="p">
	An identifier can contain only ASCII characters except for column names which can contain unicode characters.
	</p>

	</li>


	<li class="li">
	<p class="p">
	To use an identifier name that matches one of the Impala reserved keywords (listed in
	<a class="xref" href="impala_reserved_words.html#reserved_words">Impala Reserved Words</a>), surround the identifier with <code class="ph codeph">``</code>
	characters (backticks). Quote the reserved word even if it is part of a fully qualified name.
	The following example shows how a reserved word can be used as a column name if it is quoted
	with backticks in the <code class="ph codeph">CREATE TABLE</code> statement, and how the column name
	must also be quoted with backticks in a query:
	</p>

	<pre class="pre codeblock"><code>[localhost:21000] > create table reserved (`data` string);

	[localhost:21000] > select data from reserved;
	ERROR: AnalysisException: Syntax error in line 1:
	select data from reserved
	^
	Encountered: DATA
	Expected: ALL, CASE, CAST, DISTINCT, EXISTS, FALSE, IF, INTERVAL, NOT, NULL, STRAIGHT_JOIN, TRUE, IDENTIFIER
	CAUSED BY: Exception: Syntax error

	[localhost:21000] > select reserved.data from reserved;
	ERROR: AnalysisException: Syntax error in line 1:
	select reserved.data from reserved
	^
	Encountered: DATA
	Expected: IDENTIFIER
	CAUSED BY: Exception: Syntax error

	[localhost:21000] > select reserved.`data` from reserved;

	[localhost:21000] >
	</code></pre>

	<div class="note important"><span class="importanttitle">Important:</span>
	Because the list of reserved words grows over time as new SQL syntax is added,
	consider adopting coding conventions (especially for any automated scripts
	or in packaged applications) to always quote all identifiers with backticks.
	Quoting all identifiers protects your SQL from compatibility issues if
	new reserved words are added in later releases.
	</div>


	</li>


	<li class="li">
	<p class="p">
	Impala identifiers are always case-insensitive. That is, tables named <code class="ph codeph">t1</code> and
	<code class="ph codeph">T1</code> always refer to the same table, regardless of quote characters. Internally, Impala
	always folds all specified table and column names to lowercase. This is why the column headers in query
	output are always displayed in lowercase.
	</p>

	</li>

	</ul>


	<p class="p">
	See <a class="xref" href="impala_aliases.html#aliases">Overview of Impala Aliases</a> for how to define shorter or easier-to-remember aliases if the
	original names are long or cryptic identifiers.
	<span class="ph"> Aliases follow the same rules as identifiers when it
	comes to case insensitivity. Aliases can be longer than identifiers (up to the maximum
	length of a Java string) and can include additional characters such as spaces and dashes
	when they are quoted using backtick characters. </span>
	</p>


	<p class="p">
	Another way to define different names for the same tables or columns is to create views.
	See <a class="xref" href="../shared/../topics/impala_views.html#views">Overview of Impala Views</a> for details.
	</p>

	</div>

	<div class="related-links">
	<div class="familylinks">
	<div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_schema_objects.html">Impala Schema Objects and Object Names</a></div>
	</div>
	</div></body>
	</html>