spark-instrumented-optimizer/docs/sql-ref-identifier.md

---
layout: global
title: Identifiers
displayTitle: Identifiers
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  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
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---

### Description

An identifier is a string used to identify a database object such as a table, view, schema, column, etc. Spark SQL has regular identifiers and delimited identifiers, which are enclosed within backticks. Both regular identifiers and delimited identifiers are case-insensitive.

### Syntax

#### Regular Identifier

```sql
{ letter | digit | '_' } [ , ... ]
```
**Note:** If `spark.sql.ansi.enabled` is set to true, ANSI SQL reserved keywords cannot be used as identifiers. For more details, please refer to [ANSI Compliance](sql-ref-ansi-compliance.html).

#### Delimited Identifier

```sql
`c [ ... ]`
```

### Parameters

* **letter**

    Any letter from A-Z or a-z.

* **digit**

    Any numeral from 0 to 9.

* **c**

    Any character from the character set. Use <code>`</code> to escape special characters (e.g., <code>`</code>).

### Examples

```sql
-- This CREATE TABLE fails with ParseException because of the illegal identifier name a.b
CREATE TABLE test (a.b int);
org.apache.spark.sql.catalyst.parser.ParseException:
no viable alternative at input 'CREATE TABLE test (a.'(line 1, pos 20)

-- This CREATE TABLE works
CREATE TABLE test (`a.b` int);

-- This CREATE TABLE fails with ParseException because special character ` is not escaped
CREATE TABLE test1 (`a`b` int);
org.apache.spark.sql.catalyst.parser.ParseException:
no viable alternative at input 'CREATE TABLE test (`a`b`'(line 1, pos 23)

-- This CREATE TABLE works
CREATE TABLE test (`a``b` int);
```