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

Question

I have a table with two DATETIME columns   One of them is never NULL  but one of them is sometimes NULL   I need to write a query which will set all the NULL rows for column B equal to the values in column A   I have tried this example but the SQL in the selected answer does not execute because MySQL Workbench doesn t seem to like the FROM in the UPDATE

User · Answer

I don t think that other example is what you re looking for  If you re just updating one column from another column in the same table you should be able to use something like this   update some table set null column   not null column where null column is null

User · Answer

Sounds like you re working in just one table so something like this   update your table set B   A where B is null

User · Answer

I would do it this way   UPDATE YourTable SET B   COALESCE B  A     COALESCE is a function that returns its first non-null argument     In this example  if B on a given row is not null  the update is a no-op     If B is null  the COALESCE skips it and uses A instead

User · Answer

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

User · Answer

Here is sample code that might help you coping Column A to Column B   UPDATE YourTable SET ColumnB   ColumnA WHERE ColumnB IS NULL AND ColumnA IS NOT NULL

[mysql] SQL set values of one column equal to values of another column in the same table

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