Fixing the Length Issue in DolphinDB Code

Title: Fixing the Length Issue in DolphinDB Code

Dear User,

We apologize for the inconvenience caused by the length issue in your DolphinDB code. To fix this, we’ll go through the necessary adjustments to ensure that all columns have the same length.

Step 1: Identify the Columns with Different Lengths

Upon closer inspection of the original MySQL query and the translated DolphinDB code, we notice that the variable column in both queries has a different data type.

In the MySQL query:

SELECT m.*, v.monitor_type FROM m, v WHERE m.time BETWEEN 1515570908112 AND 1515657308112 AND m.variable=v.id AND v.selected=1 ORDER BY m.time;

The variable column is treated as a string. However, in the DolphinDB code:

select  m.*, monitor_type from ej(m,v,<code>variable,</code>id)
where m.time between 2018.01.10T07:55:08.112:2018.01.11T07:55:08.112 and v.selected=1 
order by  m.time

The variable column is not explicitly specified, which might cause issues due to its default data type in DolphinDB.

Step 2: Specify the Data Type for the variable Column

To resolve this issue, we need to ensure that the variable column has a consistent data type throughout both queries. Let’s modify the translated DolphinDB code as follows:

select  m.*, v.monitor_type from ej(m,v,<code>variable,</code>id string)
where m.time between 2018.01.10T07:55:08.112:2018.01.11T07:55:08.112 and v.selected=1 
order by  m.time

By explicitly specifying string as the data type for the variable column, we ensure that it matches the original MySQL query’s treatment of this column.

Step 3: Verify the Column Length

After making these adjustments, verify that all columns in both queries have the same length. You can do this by checking the data types and sizes of each column using the following commands:

In DolphinDB:

schema=select name,type from extractSchema(connection,`tbl_monitor`)
columnInfo schema.name

This will display the details of the time, id, and monitor_type columns. Verify that all these columns have the same data type and length.

Step 4: Execute the Modified Code

Finally, execute the modified DolphinDB code to verify its correctness:

db1=database("C:/dolphindb_gj/tblVariable");
db2=database("dfs://tblMonitor", RANGE, TIME_RANGE)
v=loadTable(db1,`tbl_variable);
m=loadTable(db2,"tbl_monitor"); 

select  m.*, v.monitor_type from ej(m,v,<code>variable,</code>id string)
where m.time between 2018.01.10T07:55:08.112:2018.01.11T07:55:08.112 and v.selected=1 
order by  m.time

This should resolve the length issue, and you can execute the query without encountering any errors.

If you have any further questions or concerns about this process, please feel free to ask our support team for assistance.

Best regards,

[Your Support Team]

Last modified on 2025-04-08