Question

I have 2 tables with the same columns.
for example

table 1
id
name
height
weight

table 2
id
name
height
weight

The data is table 2 is complete. But in table 1, only some data exists, and the rest of the columns are empty. for example:

          table 1    table 2
id        4          4
name      (empty)    salman
height    5'11"      5'9" 
weight    (empyy)    65kg

I want a single script, that will allow me to update the table 2 with values from table 1, but only where it exists. In places where the table 1 is empty, I want to retain the data that already exists in table 2.

I’ve tried various ways, but all required multiple queries and are long and hectic. I want to know if there is a simpler way to get this done? Preferably in a single query?

Thank you

Answer 1

You can try by joining the 2 tables and then using the CASE keyword to conditionally update the fields:

UPDATE table2 t2 INNER JOIN table1 t1 USING (id)
SET 
 t2.name = CASE WHEN (t1.name IS NULL) THEN t2.name ELSE t1.name END
 t2.height= CASE WHEN (t1.height IS NULL) THEN t2.height ELSE t1.height END
 t2.weight = CASE WHEN (t1.weight IS NULL) THEN t2.weight ELSE t1.weight END

http://dev.mysql.com/doc/refman/5.5/en/case-statement.html

http://dev.mysql.com/doc/refman/5.5/en/update.html