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| sidebar_position | sidebar_label |
|---|---|
| 33 | INSERT INTO |
INSERT INTO Statement
Inserts data into a table.
Syntax
INSERT INTO [db.]table [(c1, c2, c3)] VALUES (v11, v12, v13), (v21, v22, v23), ...
You can specify a list of columns to insert using the (c1, c2, c3). You can also use an expression with column matcher such as * and/or modifiers such as APPLY, EXCEPT, REPLACE.
For example, consider the table:
SHOW CREATE insert_select_testtable;
CREATE TABLE insert_select_testtable
(
`a` Int8,
`b` String,
`c` Int8
)
ENGINE = MergeTree()
ORDER BY a
INSERT INTO insert_select_testtable (*) VALUES (1, 'a', 1) ;
If you want to insert data in all the columns, except 'b', you need to pass so many values how many columns you chose in parenthesis then:
INSERT INTO insert_select_testtable (* EXCEPT(b)) Values (2, 2);
SELECT * FROM insert_select_testtable;
┌─a─┬─b─┬─c─┐
│ 2 │ │ 2 │
└───┴───┴───┘
┌─a─┬─b─┬─c─┐
│ 1 │ a │ 1 │
└───┴───┴───┘
In this example, we see that the second inserted row has a and c columns filled by the passed values, and b filled with value by default. It is also possible to use DEFAULT keyword to insert default values:
INSERT INTO insert_select_testtable VALUES (1, DEFAULT, 1) ;
If a list of columns does not include all existing columns, 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.
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”.
Constraints
If table has constraints, their expressions will be checked for each row of inserted data. If any of those constraints is not satisfied — server will raise an exception containing constraint name and expression, the query will be stopped.
Inserting the Results of SELECT
Syntax
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.
FORMAT clause must be specified in the end of query if SELECT clause contains table function input().
To insert a default value instead of NULL into a column with not nullable data type, enable insert_null_as_default setting.
Inserting Data from a File
Syntax
INSERT INTO [db.]table [(c1, c2, c3)] FROM INFILE file_name [COMPRESSION type] FORMAT format_name
Use the syntax above to insert data from a file stored on a client side. file_name and type are string literals. Input file format must be set in the FORMAT clause.
Compressed files are supported. Compression type is detected by the extension of the file name. Or it can be explicitly specified in a COMPRESSION clause. Supported types are: 'none', 'gzip', 'deflate', 'br', 'xz', 'zstd', 'lz4', 'bz2'.
This functionality is available in the command-line client and clickhouse-local.
Example
Execute the following queries using command-line client:
echo 1,A > input.csv ; echo 2,B >> input.csv
clickhouse-client --query="CREATE TABLE table_from_file (id UInt32, text String) ENGINE=MergeTree() ORDER BY id;"
clickhouse-client --query="INSERT INTO table_from_file FROM INFILE 'input.csv' FORMAT CSV;"
clickhouse-client --query="SELECT * FROM table_from_file FORMAT PrettyCompact;"
Result:
┌─id─┬─text─┐
│ 1 │ A │
│ 2 │ B │
└────┴──────┘
Inserting into Table Function
Data can be inserted into tables referenced by table functions.
Syntax
INSERT INTO [TABLE] FUNCTION table_func ...
Example
remote table function is used in the following queries:
CREATE TABLE simple_table (id UInt32, text String) ENGINE=MergeTree() ORDER BY id;
INSERT INTO TABLE FUNCTION remote('localhost', default.simple_table)
VALUES (100, 'inserted via remote()');
SELECT * FROM simple_table;
Result:
┌──id─┬─text──────────────────┐
│ 100 │ inserted via remote() │
└─────┴───────────────────────┘
Performance Considerations
INSERT sorts the input data by primary key and splits them into partitions by a partition key. If you insert data into several partitions at once, 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 a partition key 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.
It's also possible to asynchronously insert data in small but frequent inserts. The data from such insertions is combined into batches and then safely inserted into a table. To enable the asynchronous mode, switch on the async_insert setting. Note that asynchronous insertions are supported only over HTTP protocol, and deduplication is not supported for them.
See Also