ClickHouse DB::Exception: Bad ODBC connection string

The "DB::Exception: Bad ODBC connection string" error in ClickHouse occurs when the ODBC connection string provided for an external data source is malformed or missing required components. The BAD_ODBC_CONNECTION_STRING error code indicates that ClickHouse could not parse the connection string into a valid ODBC configuration.

Impact

The query or table creation that depends on the ODBC connection fails. No connection to the external data source is established, and no data is read or written. Existing tables and data within ClickHouse are unaffected.

Common Causes

Missing required parameters like DSN, Driver, or Server in the connection string
Incorrect syntax — for example, using commas instead of semicolons to separate key-value pairs
The DSN name referenced in the connection string is not defined in odbc.ini
Special characters in passwords or values that are not properly escaped or quoted
Mixing up ODBC connection string format with JDBC or other database connection URL formats

Troubleshooting and Resolution Steps

Review the connection string format. ODBC connection strings use semicolons to separate key-value pairs:
```
DSN=my_dsn;UID=user;PWD=password
```
or with a direct driver specification:
```
Driver={MySQL ODBC 8.0 Unicode Driver};Server=host;Database=db;UID=user;PWD=pass
```
If using a DSN, verify it is configured in your odbc.ini file:
```
cat /etc/odbc.ini
```
Or for user-level configuration:
```
cat ~/.odbc.ini
```
Test the ODBC connection outside of ClickHouse using isql:
```
isql -v my_dsn user password
```
This helps determine whether the issue is with the connection string or the ODBC driver.
When creating an ODBC dictionary or table function, ensure the connection string is properly quoted in SQL:
```
SELECT * FROM odbc('DSN=my_dsn', 'my_schema', 'my_table');
```
If the password contains special characters, wrap the value in curly braces:
```
DSN=my_dsn;UID=user;PWD={p@ss;word}
```
Verify that the ODBC driver is installed and accessible by the ClickHouse process:
```
odbcinst -q -d
```

Best Practices

Use DSN-based connections and configure them in odbc.ini to keep connection details out of SQL statements.
Test ODBC connectivity independently using command-line tools before configuring ClickHouse.
Avoid placing passwords directly in connection strings when possible; consider using ClickHouse's named collections for secrets management.
Ensure the ODBC driver and unixODBC library versions are compatible with your ClickHouse installation.
Document your ODBC configuration so team members can replicate it on other nodes.

Frequently Asked Questions

Q: What ODBC drivers does ClickHouse support?
A: ClickHouse works with any ODBC driver through the unixODBC library. Common choices include MySQL ODBC Connector, PostgreSQL ODBC (psqlODBC), and Microsoft ODBC Driver for SQL Server.

Q: Can I use a connection URL instead of a connection string?
A: No. ClickHouse ODBC functions expect a standard ODBC connection string format with semicolon-separated key-value pairs. JDBC-style URLs are not supported.

Q: How do I debug ODBC connection issues further?
A: Enable ODBC tracing in odbcinst.ini by setting Trace = Yes and TraceFile = /tmp/odbc.log. This produces detailed logs of the ODBC driver's actions, which can help identify parsing or authentication issues.