Question

Ok I have a sqlite db, that has roughly 100 rows. It is kind of a strange thing that I’m trying to do, but I need to insert a new row between each of the existing rows.

I have been trying to use the Insert statement as follows, but haven’t had any luck:

insert into t1(column1) values("hello") where id%2 == 0

So I’m basically trying to use the %-operator to tell me if the id is even or odd. For every even id number, I’d like to insert a new row.

What am I missing? What can I do differently? How can I insert a new row into every other row and have the index updated as well?

Thanks

Answer 1

Your question assumes that the rows have some kind of built-in order to them, and that you can insert rows between other rows. That’s not true.

It is true that rows have an order on disk, and that the id column is usually assigned in order, but that’s an implementation detail. When you perform a query, the database is free to return the rows in any order it chooses, unless you specify what you want with an ORDER BY clause.

Now, I’m assuming what you really want is to insert rows between the existing rows in id order. One way to get what you want would look like this:

UPDATE t1 SET id = id * 2
INSERT INTO t1 (id, column) SELECT id+1, "hello" FROM t1

The UPDATE would double the ids of all the existing rows (so 1,2,3 becomes 2,4,6); then the INSERT would perform a query on t1 and use the result to insert a new set of rows with id values one more than the existing rows (so 2,4,6 becomes 3,5,7).

I haven’t tested the above statements, so I don’t know if they would work or if they require some extra trickery (like a temporary table) since we are querying and updating the same table in one statement. Also I may have made a syntax error.