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REPLACE

The REPLACE INTO statement in Databend is used to either insert a new row into a table or update an existing row if the row already exists.

If a row with the specified conflict key(not primary key) already exists in the table, then the REPLACE INTO statement will replace the existing row with the new data. If the row doesn't exist, a new row will be inserted with the specified data.

Syntax​

REPLACE INTO <target_table> [ ( <col_name> [ , ... ] ) ]
    ON [CONFLICT] <VALUES | QUERY | STAGE>
  • <target_table>: the name of the table to insert or update data.
  • <col_name>: the column names in the table where the data will be inserted or updated.
  • <VALUES | QUERY | STAGE>: specifies how to provide the data to be inserted or updated in the columns specified.

Conflict Key in REPLACE Statement​

The conflict key is a column or combination of columns in a table that uniquely identifies a row and is used to determine whether to insert a new row or update an existing row in the table using the REPLACE INTO statement. It can be any column or combination of columns with a unique constraint, not just the primary key(Databend doesn't have primary key).

For example, in a table called employees with a unique constraint on the employee_email column, you can use the employee_email column as the conflict key in the REPLACE INTO statement like this:

REPLACE INTO employees (employee_id, employee_name, employee_salary)  ON (employee_email)
VALUES (123, 'John Doe', 50000);

Examples​

Here are some examples that show how to use the REPLACE INTO statement in Databend:

CREATE TABLE employees(id INT, name VARCHAR, salary INT);

Using VALUES​

REPLACE INTO employees (id, name, salary) ON (id)
VALUES (1, 'John Doe', 50000);
SELECT  * FROM Employees;
+------+----------+--------+
| id   | name     | salary |
+------+----------+--------+
|    1 | John Doe |  50000 |
+------+----------+--------+

Using QUERY​

In this case, the data to be inserted or updated comes from a temporary table called temp_employees:

-- Create a temp stage table
CREATE TABLE temp_employees(id INT, name VARCHAR, salary INT);
INSERT INTO temp_employees (id, name, salary) VALUES (1, 'John Doe', 60000);

REPLACE INTO employees (id, name, salary) ON (id)
SELECT id, name, salary FROM temp_employees WHERE id = 1;
SELECT  * FROM Employees;
+------+----------+--------+
| id   | name     | salary |
+------+----------+--------+
|    1 | John Doe |  60000 |
+------+----------+--------+

Using STAGE​

In this case, the data to be inserted or updated comes from a set of parquet files staged in an internal stage called employees_stage:

-- Create a internal stage
CREATE STAGE employees_stage;
-- Stage parquet files to stage
COPY INTO @employees_stage FROM 
(SELECT number, CONCAT('name-', TO_STRING(number)), number*1000 FROM numbers(10))
FILE_FORMAT = (TYPE = PARQUET);

-- Replace into with stage files
REPLACE INTO employees (id, name, salary) ON (id) 
SELECT * FROM @employees_stage (PATTERN => '.*parquet');
SELECT  * FROM Employees;
+------+--------+--------+
| id   | name   | salary |
+------+--------+--------+
|    0 | name-0 |      0 |
|    1 | name-1 |   1000 |
|    2 | name-2 |   2000 |
|    3 | name-3 |   3000 |
|    4 | name-4 |   4000 |
|    5 | name-5 |   5000 |
|    6 | name-6 |   6000 |
|    7 | name-7 |   7000 |
|    8 | name-8 |   8000 |
|    9 | name-9 |   9000 |
+------+--------+--------+