On Mon, May 16, 2011 at 12:49:14PM -0500, Nico Williams scratched on the wall: > On May 16, 2011 9:33 AM, "Simon Slavin" <slav...@bigfraud.org> wrote: > > On 16 May 2011, at 3:44am, romtek wrote: > > > > > Secondly, if I executed the above SQL code, what would happen to > triggers, > > > etc. that are associated with the original table? > > > > I suspect that's a major reason why SQLite doesn't support DROP COLUMN: > it has to check for things that might depend on the column and refuse > to DROP if it finds anything. > > Nit: that's almost certainly the reason that SQLite3 doesn't support > column rename,
I think the bigger issue is that column rename requires full understanding of the SQL statements stored in sqlite_master. To safely do a ALTER TABLE...RENAME COLUMN you have to understand the context and parts of the CREATE TABLE statement (and triggers, and indexes, and FKs of other tables). This requires a close link between the modification function, the parser, and the tokenizer. You have to scan the SQL statement and understand the different parts, and then back-trace them to a specific character in the original statement, so you know which substring to change. While this is feasible, most tokenizers and parsers are specifically designed to be abstract layers. > The row data encoding is also the reason that new columns can only > be added and appear at the end of the new CREATE TABLE statement, While I'm sure this is the major factor in that decision, the parsing issue still exists. Adding a column def to the end of a CREATE TABLE statement is fairly easy... find the last ')' character in the whole statement and insert "',' || <new column>" right before. Even if the encoding issue could be solved, inserting a column def anywhere else requires context-aware parsing and understanding of the CREATE TABLE statement, so it can be understood where the modifications have to be made. -j -- Jay A. Kreibich < J A Y @ K R E I B I.C H > "Intelligence is like underwear: it is important that you have it, but showing it to the wrong people has the tendency to make them feel uncomfortable." -- Angela Johnson _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
