INSERT-OVERWRITE

INSERT OVERWRITE

Name

INSERT OVERWRITE

Description

The function of this statement is to overwrite a table or some partitions of a table

INSERT OVERWRITE table table_name
    [ PARTITION (p1, ...) ]
    [ WITH LABEL label]
    [ (column [, ...]) ]
    [ [ hint [, ...] ] ]
    { VALUES ( { expression | DEFAULT } [, ...] ) [, ...] | query }

Parameters

table_name: the destination table to overwrite. This table must exist. It can be of the form db_name.table_name
partitions: the table partition that needs to be overwritten must be one of the existing partitions in table_name separated by a comma
label: specify a label for the Insert task
column_name: the specified destination column must be one of the existing columns in table_name
expression: the corresponding expression that needs to be assigned to a column
DEFAULT: let the column use the default value
query: a common query, the result of the query will overwrite the target.
hint: some indicator used to indicate the execution behavior of INSERT. You can choose one of this values: /*+ STREAMING */, /*+ SHUFFLE */ or `/+ NOSHUFFLE /.
STREAMING: At present, it has no practical effect and is only reserved for compatibility with previous versions. (In the previous version, adding this hint would return a label, but now it defaults to returning a label)
SHUFFLE: When the target table is a partition table, enabling this hint will do repartiiton.
NOSHUFFLE: Even if the target table is a partition table, repartiiton will not be performed, but some other operations will be performed to ensure that the data is correctly dropped into each partition.

Notice:

In the current version, the session variable enable_insert_strict is set to true by default. If some data that does not conform to the format of the target table is filtered out during the execution of the INSERT OVERWRITE statement, such as when overwriting a partition and not all partition conditions are satisfied, overwriting the target table will fail.

The INSERT OVERWRITE statement first creates a new table, inserts the data to be overwritten into the new table, and then atomically replaces the old table with the new table and modifies its name. Therefore, during the process of overwriting the table, the data in the old table can still be accessed normally until the overwriting is completed.

Example

Assuming there is a table named test. The table contains two columns c1 and c2, and two partitions p1 and p2

CREATE TABLE IF NOT EXISTS test (
  `c1` int NOT NULL DEFAULT "1",
  `c2` int NOT NULL DEFAULT "4"
) ENGINE=OLAP
UNIQUE KEY(`c1`)
PARTITION BY LIST (`c1`)
(
PARTITION p1 VALUES IN ("1","2","3"),
PARTITION p2 VALUES IN ("4","5","6")
)
DISTRIBUTED BY HASH(`c1`) BUCKETS 3
PROPERTIES (
  "replication_allocation" = "tag.location.default: 1",
  "in_memory" = "false",
  "storage_format" = "V2"
);

Overwrite Table

Overwrite the test table using the form of VALUES.

// Single-row overwrite.
INSERT OVERWRITE table test VALUES (1, 2);
INSERT OVERWRITE table test (c1, c2) VALUES (1, 2);
INSERT OVERWRITE table test (c1, c2) VALUES (1, DEFAULT);
INSERT OVERWRITE table test (c1) VALUES (1);
// Multi-row overwrite.
INSERT OVERWRITE table test VALUES (1, 2), (3, 2 + 2);
INSERT OVERWRITE table test (c1, c2) VALUES (1, 2), (3, 2 * 2);
INSERT OVERWRITE table test (c1, c2) VALUES (1, DEFAULT), (3, DEFAULT);
INSERT OVERWRITE table test (c1) VALUES (1), (3);

The first and second statements have the same effect. If the target column is not specified during overwriting, the column order in the table will be used as the default target column. After the overwrite is successful, there is only one row of data in the test table.
The third and fourth statements have the same effect. The unspecified column c2 will be overwritten with the default value 4. After the overwrite is successful, there is only one row of data in the test table.
The fifth and sixth statements have the same effect. Expressions (such as 2+2, 2*2) can be used in the statement. The result of the expression will be computed during the execution of the statement and then overwritten into the test table. After the overwrite is successful, there are two rows of data in the test table.
The seventh and eighth statements have the same effect. The unspecified column c2 will be overwritten with the default value 4. After the overwrite is successful, there are two rows of data in the test table.

Overwrite the test table in the form of a query statement. The data format of the test2 table and the test table must be consistent. If they are not consistent, implicit data type conversion will be triggered.
```
INSERT OVERWRITE table test SELECT * FROM test2;
INSERT OVERWRITE table test (c1, c2) SELECT * from test2;
```

The first and second statements have the same effect. The purpose of these statements is to take data from the test2 table and overwrite the test table with the taken data. After the overwrite is successful, the data in the test table will be consistent with the data in the test2 table.

Overwrite the test table and specify a label.

INSERT OVERWRITE table test WITH LABEL `label1` SELECT * FROM test2;
INSERT OVERWRITE table test WITH LABEL `label2` (c1, c2) SELECT * from test2;

Users can use the SHOW LOAD; command to check the status of the job imported by this label. It should be noted that the label is unique.

Overwrite Table Partition

When using INSERT OVERWRITE to rewrite partitions, we actually encapsulate the following three steps into a single transaction and execute it. If it fails halfway through, the operations that have been performed will be rolled back:

Assuming that partition p1 is specified to be rewritten, first create an empty temporary partition pTMP with the same structure as the target partition to be rewritten.
Write data to pTMP.
replace p1 with the pTMP atom

The following is examples:

Overwrite partitions P1 and P2 of the test table using the form of VALUES.

// Single-row overwrite.
INSERT OVERWRITE table test PARTITION(p1,p2) VALUES (1, 2);
INSERT OVERWRITE table test PARTITION(p1,p2) (c1, c2) VALUES (1, 2);
INSERT OVERWRITE table test PARTITION(p1,p2) (c1, c2) VALUES (1, DEFAULT);
INSERT OVERWRITE table test PARTITION(p1,p2) (c1) VALUES (1);
// Multi-row overwrite.
INSERT OVERWRITE table test PARTITION(p1,p2) VALUES (1, 2), (4, 2 + 2);
INSERT OVERWRITE table test PARTITION(p1,p2) (c1, c2) VALUES (1, 2), (4, 2 * 2);
INSERT OVERWRITE table test PARTITION(p1,p2) (c1, c2) VALUES (1, DEFAULT), (4, DEFAULT);
INSERT OVERWRITE table test PARTITION(p1,p2) (c1) VALUES (1), (4);

Unlike overwriting an entire table, the above statements are overwriting partitions in the table. Partitions can be overwritten one at a time or multiple partitions can be overwritten at once. It should be noted that only data that satisfies the corresponding partition filtering condition can be overwritten successfully. If there is data in the overwritten data that does not satisfy any of the partitions, the overwrite will fail. An example of a failure is shown below.

INSERT OVERWRITE table test PARTITION(p1,p2) VALUES (7, 2);

The data overwritten by the above statements (c1=7) does not satisfy the conditions of partitions P1 and P2, so the overwrite will fail.

Overwrite partitions P1 and P2 of the test table in the form of a query statement. The data format of the test2 table and the test table must be consistent. If they are not consistent, implicit data type conversion will be triggered.
```
INSERT OVERWRITE table test PARTITION(p1,p2) SELECT * FROM test2;
INSERT OVERWRITE table test PARTITION(p1,p2) (c1, c2) SELECT * from test2;
```

Overwrite partitions P1 and P2 of the test table and specify a label.

INSERT OVERWRITE table test PARTITION(p1,p2) WITH LABEL `label3` SELECT * FROM test2;
INSERT OVERWRITE table test PARTITION(p1,p2) WITH LABEL `label4` (c1, c2) SELECT * from test2;

Keywords

INSERT OVERWRITE