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Connection tips

Initial SQL tab​

If the Set Session ID checkbox is activated on the Advanced tab (by default), feel free to set session level settings using

SET my_setting=value;

Advanced tab​

In 99% of cases you don't need the Advanced tab, for the remaining 1% you can use the following settings:

  • Custom Connection Parameters. By default, socket_timeout is already specified, this parameter may need to be changed if some extracts are updated for a very long time. The value of this parameter is specified in milliseconds. The rest of the parameters can be found here, add them in this field separated by commas

  • JDBC Driver custom_http_params. This field allows you to drop some parameters into the ClickHouse connection string by passing values to the custom_http_params parameter of the driver. For example, this is how session_id is specified when the Set Session ID checkbox is activated

  • JDBC Driver typeMappings. This field allows you to pass a list of ClickHouse data type mappings to Java data types used by the JDBC driver. The connector automatically displays large Integers as strings thanks to this parameter, you can change this by passing your mapping set (I do not know why) using

    UInt256=java.lang.Double,Int256=java.lang.Double

    Read more about mapping in the corresponding section

  • JDBC Driver URL Parameters. You can pass the remaining driver parameters, for example jdbcCompliance, in this field. Be careful, the parameter values must be passed in the URL Encoded format, and in the case of passing custom_http_params or typeMappings in this field and in the previous fields of the Advanced tab, the values of the preceding two fields on the Advanced tab have a higher priority

  • Set Session ID checkbox. It is needed to set session-level settings in Initial SQL tab, generates a session_id with a timestamp and a pseudo-random number in the format "tableau-jdbc-connector-{timestamp}-{number}"

Limited support for UInt64, Int128, (U)Int256 data types​

By default, the driver displays fields of types UInt64, Int128, (U)Int256 as strings, but it displays, not converts. This means that when you try to write the next calculated field, you will get an error

LEFT([myUInt256], 2) // Error!

In order to work with large Integer fields as with strings, it is necessary to explicitly wrap the field in the STR() function

LEFT(STR([myUInt256]), 2) // Works well!

However, such fields are most often used to find the number of unique values (IDs as Watch ID, Visit ID in Yandex.Metrika) or as a Dimension to specify the detail of the visualization, it works well.

COUNTD([myUInt256]) // Works well too!

When using the data preview (View data) of a table with UInt64 fields, an error does not appear now.