I found out just yesterday that Postfix uses a new syntax for SQL lookups. It seems like my old syntax was still compatible with Postfix 2.2.8. I guess it will be backward compatible for a while.
For Postfix 2.2 and later :
user = someone password = password dbname = database query = SELECT alias FROM alias_table WHERE alias='%s'
For Postfix releases prior to 2.2 :
user = someone password = password dbname = database select_field = alias table = alias_table where_field = alias
Meaning of the ‘%’ :
%s This is replaced by the input key. SQL quoting is used to make sure that the input key does not add unexpected metacharacters.
A word on backward compatibility :
As of Postfix 2.2 this interface is obsolete, it is replaced by the more general query interface described above. If the query parameter is defined, the legacy parameters are ignored. Please migrate to the new inter- face as the legacy interface may be removed in a future release.