> ## Documentation Index
> Fetch the complete documentation index at: https://ngquct-docs-fix-500-query-results.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# ClickHouse
> Connection settings, the URL format, and the parts and partition tools for ClickHouse
Every query travels over HTTP to port 8123. The native TCP protocol on 9000 is not used, so the server's HTTP interface has to be on. Any version connects, though data-skipping indices need 19.17 or newer to show up. The driver ships inside the app.
## Quick setup
Click **Create Connection…**, select **ClickHouse**, fill in host, port, and credentials, then click **Save & Connect**.
## Connection settings
| Field | Default | Notes |
| ------------ | ----------- | ----------------------------------------------------------- |
| **Host** | `localhost` | |
| **Port** | `8123` | HTTP port, not 9000 native TCP |
| **Username** | `default` | Left empty, `default` is sent. Set a password in production |
| **Database** | `default` | Optional. Leave empty and the server uses `default` |
Switching database happens in place, with no reconnect, and the sidebar's choice only affects new tabs: an open tab stays on its own database. See [Tabs](/features/tabs#where-a-tab-points). For unencrypted HTTP to a remote server, use [SSH tunneling](/connections/ssh-tunneling).
## Connection URL
```text theme={null}
clickhouse://user:password@host:8123/database
```
See [Connection URL Reference](/connections/urls) for all parameters.
## Browsing
The sidebar lists the current database's tables, views, and materialized views. Press `Cmd+K` or click the database name in the toolbar to switch. Choose **View > Sidebar as Tree** to list every database and expand them in place.
| Tab | Contents |
| ------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Structure** | Columns with types, default expressions, and comments |
| **Indexes** | The sorting key, listed as `PRIMARY (sorting key)`, plus data-skipping indices (minmax, set, bloom\_filter, and the rest) |
| **DDL** | The full `CREATE TABLE`, engine and settings included |
| **Parts** | Every part from `system.parts` with its partition, rows, disk size, modification time, and active flag, plus **Optimize**, **Drop Partition**, and **Detach Partition** |
The [Server Dashboard](/features/server-dashboard) covers ClickHouse with active sessions, server metrics, and slow queries.
## EXPLAIN variants
Click the Explain dropdown in the query editor to choose:
| Variant | Description |
| ------------ | ----------------------------------------------------- |
| **Plan** | Logical query plan (default) |
| **Pipeline** | Physical execution pipeline with thread and port info |
| **AST** | Abstract syntax tree of the parsed query |
| **Syntax** | Query after syntax optimizations |
| **Estimate** | Estimated rows, marks, and parts to read |
## Running queries
Each request carries a query id and asks for progress in the HTTP headers, so a long query reports rows read as it goes. Cancelling sends `KILL QUERY` for that id, stopping the query on the server rather than only dropping the connection. The [query timeout](/customization/general-settings#query-timeout) bounds each request at the timeout plus 30 seconds.
Grid edits go out as INSERT, `ALTER TABLE … UPDATE`, and `ALTER TABLE … DELETE`.
ClickHouse mutations run in the background, so the grid reports the statement as accepted rather than applied, and a large table can take a long time. Watch `SELECT * FROM system.mutations WHERE is_done = 0` for progress.
## SSL/TLS
The default is **Disabled**, which sends plain HTTP. Any other mode switches the URL scheme to `https`.
| Mode | Verifies | Pick it for |
| --------------------------- | ---------------------------------------------------------- | ------------------------------------------------- |
| **Preferred**, **Required** | Nothing. Encryption only | A self-signed certificate you have no CA file for |
| **Verify CA** | The chain, against the CA file | Private PKI |
| **Verify Identity** | The chain and the hostname, against the system trust store | ClickHouse Cloud, on port 8443 |
The CA file may be PEM or DER. If **Verify CA** cannot read it, the connection fails rather than falling back to the public root store. See [SSL/TLS](/connections/ssl).
## Limitations
* No foreign keys and no multi-statement transactions.
* No auto-increment, and the primary key and sorting key are fixed at creation. Structure editing covers adding, modifying, and dropping columns and data-skipping indexes; recreate the table for anything else.
* A `SET` does not carry to the next statement. Every statement is its own HTTP request with no session id, and the setting is gone by the next one. Put it in a `SETTINGS` clause on the query itself.
* A query with its own `FORMAT` clause, such as `SELECT 1 FORMAT JSON`, shows the server's raw output in one column instead of a parsed table. Drop the clause to get a grid.
## Troubleshooting
**Connection refused**: `curl http://localhost:8123/ping` should answer `Ok.`. The usual cause is the port: 8123 is HTTP, 8443 HTTPS, 9000 native TCP and unused here. If the HTTP interface is off, check `` in `/etc/clickhouse-server/config.xml`.
**Authentication failed (HTTP 403)**: Check the user exists (`SELECT name, auth_type FROM system.users`) and reaches the target database (`SHOW GRANTS FOR app_user`).
**Connection timeout**: Check host, port, firewall rules, and, on ClickHouse Cloud, that your IP is in the allowed list.