Sometimes we have to apply simple operations in multiple columns and modify the stored/original value of those columns. ClickHouse® has SELECT modifiers that can help us: APPLY, EXCEPT AND REPLACE.
Let’s see some easy examples using this simple set:
The first one APPLY will apply a function to all the columns we specify in the SELECT clause like:
Now, with EXCEPT we can select different columns except the ones specified, and we can combine the modifiers:
The last one is REPLACE that you can use again apply simple visual functions and replace columns with new values, using alias expressions:
Sweet right? well as we said you can mix them all like this:
or this,
And stay tuned for the next ClickHouse® release 21.10 in which we can use a lambda function inside an APPLY.
