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* Update of english version of descriprion of the table function `file`. * New syntax for ReplacingMergeTree. Some improvements in text. * Significantly change article about SummingMergeTree. Article is restructured, text is changed in many places of the document. New syntax for table creation is described. * Descriptions of AggregateFunction and AggregatingMergeTree are updated. Russian version. * New syntax for new syntax of CREATE TABLE * Added english docs on Aggregating, Replacing and SummingMergeTree. * CollapsingMergeTree docs. English version. * 1. Update of CollapsingMergeTree. 2. Minor changes in markup * Update aggregatefunction.md * Update aggregatefunction.md * Update aggregatefunction.md * Update aggregatingmergetree.md * GraphiteMergeTree docs update. New syntax for creation of Replicated* tables. Minor changes in *MergeTree tables creation syntax. * Markup fix * Markup and language fixes * Clarification in the CollapsingMergeTree article
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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.