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cassandracqlcql3

Difference between UPDATE and INSERT in Cassandra?

What is the difference between UPDATE and INSERT when executing CQL against Cassandra?

It looks like there used to be no difference, but now the documentation says that INSERT does not support counters while UPDATE does.

Is there a "preferred" method to use? Or are there cases where one should be used over the other?

Thanks so much!

Solution

  • Counter Columns in Cassandra couldn't be set to an arbitrary value: they can only be incremented or decremented by any arbitrary value.

    For this reason, INSERT doesn't support Counter Column because you cannot "insert" a value into a Counter Column. You can only UPDATE them (increment or decrement) by some value. Here's how you would update a Counter column.

        UPDATE ... SET name1 = name1 + <value>

    You asked:

    Is there a "preferred" method to use? Or are there cases where one should be used over the other?

    Yes. If you are inserting values to the database, you can use INSERT. If the column doesn't exists, it will be created for you. Otherwise, INSERT's effect is similar to UPDATE. INSERT is useful when you don't have a pre-designed schema (Dynamic Column Family, i.e. insert anything, anytime). If you are designing the schema before hand (Static Column Family, similar to RDMS) and know each column, then you can use UPDATE.