仅当字段为空时将列复制到另一列

Question

I have an SQL question which may be basic to some but is confusing me. Here is an example of a table:

buu_properties_products (price, years, area, covered_area)

Now I want to copy the area column fields into the covered_area fields but only if the covered_area field is empty.

I have almost 1000 products in this table and I need to update those column without deleting the covered_area values when they are present.

I am running MySQL 5.1

Answer 1

Depends what 'empty' means. If it means NULL :

UPDATE buu_properties_products
SET covered_area = area
WHERE covered_area IS NULL

If it means an empty string:

UPDATE buu_properties_products
SET covered_area = area
WHERE covered_area = ''

If it means either:

UPDATE buu_properties_products
SET covered_area = area
WHERE covered_area IS NULL OR covered_area = ''