ClickHouse allows sending a server the data that is needed for processing a query, together with a `SELECT` query. This data is put in a temporary table (see the section “Temporary tables”) and can be used in the query (for example, in `IN` operators).
For example, if you have a text file with important user identifiers, you can upload it to the server along with a query that uses filtration by this list.
If you need to run more than one query with a large volume of external data, do not use this feature. It is better to upload the data to the DB ahead of time.
One of the following parameters is required:**–types** – A list of comma-separated column types. For example: `UInt64,String`. The columns will be named _1, _2, ...
The files specified in ‘file’ will be parsed by the format specified in ‘format’, using the data types specified in ‘types’ or ‘structure’. The table will be uploaded to the server and accessible there as a temporary table with the name in ‘name’.
$ cat /etc/passwd | sed 's/:/\t/g' | clickhouse-client --query="SELECT shell, count() AS c FROM passwd GROUP BY shell ORDER BY c DESC" --external --file=- --name=passwd --structure='login String, unused String, uid UInt16, gid UInt16, comment String, home String, shell String'
When using the HTTP interface, external data is passed in the multipart/form-data format. Each table is transmitted as a separate file. The table name is taken from the file name. The `query_string` is passed the parameters `name_format`, `name_types`, and `name_structure`, where `name` is the name of the table that these parameters correspond to. The meaning of the parameters is the same as when using the command-line client.