SQL sets the values ​​of one column equal to the values ​​of another column in the same table

Question

I have a table with two DATETIME columns.

One of them never has NULL, but one of them sometimes is NULL.

I need to write a query that will set all NULL rows for column B to the same values ​​in column A.

I tried this example , but SQL in the selected answer fails because MySQL Workbench does not seem to like FROM in UPDATE.

Answer 1

It looks like you only work in one table, so something like this:

update your_table set B = A where B is null 

Answer 2

 UPDATE YourTable SET ColumnB=ColumnA WHERE ColumnB IS NULL AND ColumnA IS NOT NULL 

Answer 3

I would do it like this:

 UPDATE YourTable SET B = COALESCE(B, A); 

COALESCE is a function that returns its first nonzero argument.

In this example, if B in the given string is not null, the update is no-op.

If B is null, COALESCE skips it and uses A. instead.

Answer 4

I do not think another example is what you are looking for. If you are just updating one column from another column in the same table, you should use something like this.

 update some_table set null_column = not_null_column where null_column is null 

Answer 5

Here is sample code that can help you copy column A to column B:

 UPDATE YourTable SET ColumnB = ColumnA WHERE ColumnB IS NULL AND ColumnA IS NOT NULL;