Null substitution in SQLite:

问题:

In Sybase and MSSqlServer TransactSQL, we have a function IsNull(columnName,valueForNull) to return a typed default value when a column value is null. How can I replicate this functionality in SQLite?

Example in TransactSQL:

select IsNull(MyColumn,-1) as MyColumn from MyTable

If MyColumn is null, this expression will return -1 as the value of MyColumn. Want to do something similar in SQLite.

(Yes, I know I can write my own wrapper function to handle this - that's not the answer I'm looking for)

TIA

回答1:

You can use ifnull:

select ifnull(MyColumn,-1) as MyColumn from MyTable

回答2:

You should use the standard COALESCE function:

select coalesce(MyColumn, -1) as MyColumn from MyTable

Any database that understands standard ANSI SQL will support COALESCE so using it is a good habit to get into.

回答3:

The SQL standard way to do this is with CASE:

 SELECT CASE WHEN MyColumn IS NULL THEN -1 ELSE MyColumn END FROM MyTable

Considerably more verbose than engine-specific IFNULL, ISNULL, NZ functions, but more portable.

(Or, as mu points out, you can use the much better COALESCE for this).

回答4:

SQLite has the IFNULL() built-in function which would do what I think you're trying here.