Hi Zhengguo,
This is a very valuable feature.
Before Doris supports syntax of update, although Doris can also update data
indirectly through the uniq model, it is very cumbersome to use.
The user is required to retain the full amount of new data.
If necessary, I have a better understanding of the query layer, and I can
do development to support the update function.
Ling Miao
寒江雪 <yangz...@gmail.com> 于2021年1月20日周三 下午3:14写道：
> ## Background
>
> The current Doris table does not support the update operation, but there
> are many scenarios where the data needs to be updated. Due to the batch
> delete function we implemented before, it paved the way for the update.
>
> ## Syntax
>
> We only support single table update
>
> ```
> UPDATE table_name
> SET assignment_list
> [WHERE where_condition]
> [ORDER BY...]
> [LIMIT row_count]
>
> value:
> {expr | DEFAULT}
>
> assignment:
> col_name = value
>
> assignment_list:
> assignment [, assignment].
> ```
>
> ## Design
>
> There are two kinds of updates involved here, one that only contains the
> value column, and the other that contains the key column.
>
> * Include and update of value column
>
> This method is relatively simple. You only need to plan the update
> statement into a query plan like `select * from table insert into table`
> during query planning, and you need to add an update node to modify the
> data to the updated value, or plan Into a statement similar to `select a,
> b,'xx','xx1' from table insert into table` and hand it directly to the
> tableSink node
>
> * Contains the update of the key column
>
> This kind of relatively complicated, we need to divide the query into two
> parts, and need to use the MERGE semantics in the batch delete, first plan
> it into a query plan similar to `select * from table insert into table`,
> and then generate it first for the modification of the key column One piece
> of data that needs to be deleted, and then replace the value of the key
> column to generate new data that needs to be added, mainly generating two
> pieces of imported data from one piece of original data. Need update node
> to have the ability to repeat data
>
> ## Subtasks
>
> 1. Add index to unique table value column to speed up data scanning
> 2. FE supports update statements and generates corresponding query plans.
> Be implements update node, which can be divided into two parts here
> 1. Support updates that only contain the value column
> 2. Support the update of the key column
>
