MSSQL：如果有条件，则使用另一列中的值有条件地填充该列

Question

This is the logic I'm trying to implement:

If 'new_column' is blank then pull in the value from the 'event' column ... otherwise leave the value as is in 'new_column'

I have written it successfully in Python code but am new to SQL.

df_EVENT5_6['new_column'] = np.where(df_EVENT5_6['new_column'] == '', df_EVENT5_6['event'], df_EVENT5_6['new_column'])

How do I translate the above Python code to SQL?

Answer 1

This is how you can replace blanks in MSSQL:

SELECT REPLACE(new_column, '', event)
FROM TABLE

If you also want to take care of NULLS then you can add ISNULL in same query:

SELECT REPLACE(ISNULL(new_column, event), '', event)
FROM TABLE

Answer 2

您在寻找coalesce()吗？

select coalesce(new_column, event) as new_column

Answer 3

Assuming you're trying to RETURN the data, you would use a the COALESCE function in a SELECT statement, as seen below:

select
    [new_column] = coalesce(new_column, event),
    [event] = event
from
    df_EVENT;

What COALESCE does is take arguments in order of precedence and returns the first value that is NOT NULL. Underneath this function it is evaluated as a CASE expression, so you could amend the above for NULL with your condition for Empty-Length strings as such:

select
    [new_column] = case when new_column > '' then new_column else event end
    [event] = event
from
    df_EVENT;

This is without knowing your data source. If you are doing an INSERT from Python, then you could keep your Python logic and apply it to the SQL statement that is passed. Otherwise, you could do as I listed above.

Answer 4

Try this if you using Sql server

Insert into TABLENAME (Column1)
(Select ISNULL(new_column, eventcolumn) from TABLENAME)

ISNULL function check thats if new_column is null then takes value of eventcolum else take new column value

Or You also can use case when facility of sql. Case when syntax like this :

Select case when isnull(new_column,'') = '' Then eventcolumn else new_column end