DML

Is used to manipulate data stored in a database.

INSERT

tip

CnosDB requires the inserted data columns to have a timestamp and the VALUES list must be constant. If a column is not selected, the value is NULL.

The time column cannot be NULL, TAG column and FIELD column can be NULL.

For example, INSERT INTO air (TIME, station, visibility) VALUES(1666132800000000000, NULL, NULL)

If the VALUES list needs an expression, use the INSERT SELECT syntax.

INSERT [INTO] tb_name [ ( column_name [, ...] ) ] VALUES (  const [, ...] ) [, ...] | select_statment;

View the INSERT example

Insert a record.

INSERT INTO air (TIME, station, visibility, temperature, pressure) VALUES(now(), 'XiaoMaiDao', 56, 69, 77);

Insert multiple records.

INSERT INTO air (TIME, station, visibility, temperature, pressure) VALUES
                ('2022-10-19 05:40:00', 'XiaoMaiDao', 55, 68, 76), 
                ('2022-10-19 04:40:00', 'XiaoMaiDao', 55, 68, 76);

Insert records based on query results.

1. Create a new table.

CREATE TABLE air_visibility (
    visibility DOUBLE,
    TAGS(station)
);

2. Insert records into air_visibility based on query results.

INSERT air_visibility (TIME, station, visibility) SELECT TIME, station, visibility FROM air;

UPDATE

tip

Cannot update TAG column and FIELD column simultaneously.

CnosDB supports updating TAG column values to NULL.

value_expression can only be an expression with a value that can be determined at compile time, such as: 'constant', '1 + 2', 'CAST('1999-12-31 00:00:00.000' as timestamp)' etc.

where_clause cannot contain field column or time column, must not be empty, if you want to update all data in the table, use 'where true', which means you accept the performance issues when the table data is large.

Cannot modify to an existing series (all TAG column values form a series).

Avoid performing TAG operations when writing data, as it may cause series conflicts.

UPDATE table_name SET ( assignment_clause [, ...] ) where_clause

assignment clause :
    tag_name = value_expression

View the UPDATE example

Update the data in the TAG column of the air table, changing records that meet the condition station = 'LianYunGang' to station = 'ShangHai'.

UPDATE air SET station = 'ShangHai' where station = 'LianYunGang';

Update Data by Time and Numerical Range

UPDATE air SET pressure = pressure + 100 where pressure = 68 and time < '2023-01-14T16:03:00';

DELETE

tip

Cannot delete data with FIELD type columns as conditions.

DELETE FROM table_name where_clause

View the DELETE example

Using TAG type columns and time as conditions

DELETE FROM air WHERE station = 'LianYunGang' and time < '2023-01-14T16:03:00';

Using FIELD type columns as conditions

DELETE FROM air WHERE temperature > 0;

The following results will be returned:

422 Unprocessable Entity, details: {"error_code":"010005","error_message":"This feature is not implemented: Filtering on the field column on the tskv table in delete statement"}