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* Some improvements for introduction/performance.md
* Minor improvements for example_datasets
* Add website/package-lock.json to .gitignore
* YT paragraph was badly outdated and there is no real reason to write a new one
* Use weird introduction article as a starting point for F.A.Q.
* Some refactoring of first half of ya_metrika_task.md
* minor
* Weird docs footer bugfix
* Forgotten redirect
* h/v scrollbars same size in docs
* CLICKHOUSE-3831: introduce security changelog
* A bit more narrow tables on docs front page
* fix flag in ru docs
* Save some space in top level of docs ToC
* Capitalize most words in titles of docs/en/
* more docs scrollbar fixes
* fix incorrect merge
* fix link
* fix switching languages in single page docs mode
* Update mkdocs & mkdocs-material + unminify javascript
* cherrypick 17e18d1ecc
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INSERT
Adding data.
Basic query format:
INSERT INTO [db.]table [(c1, c2, c3)] VALUES (v11, v12, v13), (v21, v22, v23), ...
The query can specify a list of columns to insert [(c1, c2, c3)]. In this case, the rest of the columns are filled with:
- The values calculated from the
DEFAULTexpressions specified in the table definition. - Zeros and empty strings, if
DEFAULTexpressions are not defined.
If strict_insert_defaults=1, columns that do not have DEFAULT defined must be listed in the query.
Data can be passed to the INSERT in any format supported by ClickHouse. The format must be specified explicitly in the query:
INSERT INTO [db.]table [(c1, c2, c3)] FORMAT format_name data_set
For example, the following query format is identical to the basic version of INSERT ... VALUES:
INSERT INTO [db.]table [(c1, c2, c3)] FORMAT Values (v11, v12, v13), (v21, v22, v23), ...
ClickHouse removes all spaces and one line feed (if there is one) before the data. When forming a query, we recommend putting the data on a new line after the query operators (this is important if the data begins with spaces).
Example:
INSERT INTO t FORMAT TabSeparated
11 Hello, world!
22 Qwerty
You can insert data separately from the query by using the command-line client or the HTTP interface. For more information, see the section "Interfaces".
Inserting The Results of SELECT
INSERT INTO [db.]table [(c1, c2, c3)] SELECT ...
Columns are mapped according to their position in the SELECT clause. However, their names in the SELECT expression and the table for INSERT may differ. If necessary, type casting is performed.
None of the data formats except Values allow setting values to expressions such as now(), 1 + 2, and so on. The Values format allows limited use of expressions, but this is not recommended, because in this case inefficient code is used for their execution.
Other queries for modifying data parts are not supported: UPDATE, DELETE, REPLACE, MERGE, UPSERT, INSERT UPDATE.
However, you can delete old data using ALTER TABLE ... DROP PARTITION.
Performance Considerations
INSERT sorts the input data by primary key and splits them into partitions by month. If you insert data for mixed months, it can significantly reduce the performance of the INSERT query. To avoid this:
- Add data in fairly large batches, such as 100,000 rows at a time.
- Group data by month before uploading it to ClickHouse.
Performance will not decrease if:
- Data is added in real time.
- You upload data that is usually sorted by time.