---
title: UNKNOWN_IDENTIFIER ClickHouse error
meta:
  description: Learn how to fix the UNKNOWN_IDENTIFIER error in ClickHouse and Tinybird. Understand what causes it and see examples of how to resolve it
---

# UNKNOWN_IDENTIFIER ClickHouse error

{% callout %}
This error usually means you're referencing a column, table, or function that doesn't exist. Check your spelling and make sure the referenced object exists in your schema.
{% /callout %}

The `UNKNOWN_IDENTIFIER` error in ClickHouse (and Tinybird) happens when you reference a column, table, function, or other identifier that doesn't exist in the current context. This is the most common error users encounter when writing SQL queries.

## What causes this error

You'll typically see it when:

* Referencing a column that doesn't exist in the table
* Calling a function that doesn't exist or is misspelled
* Using an alias that hasn't been defined
* Referencing a variable or parameter that doesn't exist
* Referencing a non-existent column in CTEs or subqueries

{% callout type="caution" %}
**Note**: Using a table name that doesn't exist typically throws a `UNKNOWN_TABLE` error (code 60), not `UNKNOWN_IDENTIFIER`.
{% /callout %}

## Example errors

```sql {% title="Fails: column doesn't exist" %}
SELECT user_id, email, non_existent_column FROM events
```

```sql {% title="Fails: table doesn't exist" %}
SELECT * FROM non_existent_table
```

```sql {% title="Fails: function doesn't exist" %}
SELECT non_existent_function(column) FROM events
```

{% callout type="caution" %}
**Note**: The table example above actually throws a `UNKNOWN_TABLE` error (code 60), not `UNKNOWN_IDENTIFIER`. This is because ClickHouse distinguishes between unknown tables and unknown identifiers within existing tables.
{% /callout %}

```sql {% title="Fails: undefined alias" %}
SELECT user_id, COUNT(*) as count FROM events GROUP BY user_id HAVING count > 10
```

## How to fix it

### Check column names

Use the system.columns table to see what columns exist:

```sql {% title="Check table structure" %}
SELECT * FROM system.columns WHERE table = 'events'
```

### Check table names

List all tables in your database:

```sql {% title="List all tables" %}
SELECT * FROM system.tables
```

### Check function names

Verify function names in the ClickHouse documentation or use the system.functions table:

```sql {% title="List available functions" %}
SELECT * FROM system.functions WHERE name LIKE '%date%'
```



## Common patterns and solutions

### Case sensitivity

ClickHouse is case-sensitive. Make sure your identifiers match exactly:

```sql {% title="Wrong: wrong case" %}
SELECT User_ID FROM events
```

```sql {% title="Correct: proper case" %}
SELECT user_id FROM events
```

### Schema qualification

If you have multiple databases, qualify your table names:

```sql {% title="Qualify with database name" %}
SELECT * FROM my_database.events
```

### Check for typos

Common typos that cause this error:
* `user_id` vs `userid`
* `created_at` vs `createdat`
* `timestamp` vs `time_stamp`

### Helpful error messages

ClickHouse often provides helpful suggestions in UNKNOWN_IDENTIFIER errors:

```sql {% title="Error with suggestion" %}
SELECT User_ID FROM events
-- Error: Unknown expression identifier `User_ID` in scope SELECT User_ID FROM events.
-- Maybe you meant: ['user_id']
```

### Common Table Expressions (CTEs)

When using CTEs with `WITH`, referencing non-existent columns can cause UNKNOWN_IDENTIFIER errors:

```sql {% title="Wrong: referencing non-existent column in CTE" %}
WITH user_stats AS (
    SELECT user_id, COUNT(*) as count FROM events GROUP BY user_id
)
SELECT non_existent_column FROM user_stats
```

```sql {% title="Correct: reference only existing columns" %}
WITH user_stats AS (
    SELECT user_id, COUNT(*) as count FROM events GROUP BY user_id
)
SELECT user_id, count FROM user_stats WHERE user_id > 10
```

## Tinybird-specific notes

In Tinybird, this error often occurs when:

* Referencing columns that don't exist in your Data Source schema
* Using table names that don't match your Data Source names
* Referencing Pipes that haven't been created yet

## See also

* [ClickHouse Data Types](/sql-reference/data-types)
* [Working with Data Sources](/forward/get-data-in/data-sources)
* [Common function errors](/sql-reference/clickhouse-errors/UNKNOWN_FUNCTION)