CODEWITHSUNDEEP
pythonsqlpython-2.7sqlitesql-update
Ralk
Ralk

Reputation: 461

Updating only non-null rows

I'm pretty new to SQL and I was wondering if I can update a column using a condition.

I have two columns, and I want to update the second one (B) only if there is something in the first one (A) :

'UPDATE Table1 SET ColumnB = (SELECT BG FROM Table2 WHERE Table1.ColumnC = BG.ColumnZ)'

How can I avoid to apply the update to the rows where column A is null ?

Upvotes: 0

Views: 95

Answers (1)

Gordon Linoff
Gordon Linoff

Reputation: 1271031

One method uses EXISTS, if you only want to update where there is a match:

UPDATE Table1 
    SET ColumnB = (SELECT BG FROM Table2 t2 WHERE table1.ColumnC = t2.ColumnZ)
    WHERE EXISTS ( SELECT BG FROM Table2 t2 WHERE table1.ColumnC = t2.ColumnZ );

If you want to update only where the first table has a non-NULL value, then use WHERE in the outer query:

UPDATE Table1 
    SET ColumnB = (SELECT BG FROM Table2 t2 WHERE table1.ColumnC = t2.ColumnZ)
    WHERE ColumnB IS NOT NULL;

Upvotes: 2

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