docs/sql-ref-identifier.md

---
layout: global
title: Identifiers
displayTitle: Identifiers
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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.enforceReservedKeywords` 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>).

### Reserved system names

`system`, `session`, and `builtin` have special meaning and should not be used as user-defined
catalog or schema names.

| Name | Position | Notes |
| :--- | :------- | :---- |
| `system` | catalog | Virtual catalog hosting `system.builtin` and `system.session`. Spark does not load `system` through the v2 catalog API; setting `spark.sql.catalog.system = ...` is unsupported and produces undefined results. The current catalog cannot be `system`. |
| `builtin` | schema | A persistent schema named `builtin` is allowed but discouraged because it collides with `system.builtin`. |
| `session` | schema | A persistent schema named `session` is allowed but discouraged because it collides with `system.session`. |

A partially qualified 2-part reference like `builtin.x` or `session.x` walks a small **mini-path** to
choose the implicit catalog: by default it resolves to `system.builtin.x` / `system.session.x`
if such an object exists, and otherwise falls back to the same name in the current catalog. So
an object in a persistent `builtin` or `session` schema is shadowed only when an object of the
same name exists in the corresponding system namespace. The shadowed object stays reachable via its fully qualified 3-part name (for example
`spark_catalog.session.x`). Set `spark.sql.legacy.persistentCatalogFirst` to `true` to reverse
the preference: the current catalog is tried first and the system namespace becomes the fallback.

The `system.builtin` and `system.session` namespaces are described in
[SET PATH](sql-ref-syntax-aux-conf-mgmt-set-path.html). Temporary objects in `system.session` are
documented under [CREATE VIEW](sql-ref-syntax-ddl-create-view.html) and
[CREATE FUNCTION (SQL)](sql-ref-syntax-ddl-create-sql-function.html).

### Examples

```sql
-- This CREATE TABLE fails with ParseException because of the illegal identifier name a.b
CREATE TABLE test (a.b int);
Error in query:
[PARSE_SYNTAX_ERROR] Syntax error at or near '.': extra input '.'(line 1, pos 20)

== SQL ==
CREATE TABLE test (a.b int)
--------------------^^^

-- 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);
Error in query:
[PARSE_SYNTAX_ERROR] Syntax error at or near '`'(line 1, pos 24)

== SQL ==
CREATE TABLE test1 (`a`b` int)
------------------------^^^

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