SQLite Modify Column

问题:

I need to modify a column in a SQLite database but I have to do it programatically due to the database already being in production. From my research I have found that in order to do this I must do the following.

• Create a new table with new schema
• Copy data from old table to new table
• Drop old table
• Rename new table to old tables name

That seems like a ridiculous amount of work for something that should be relatively easy. Is there not an easier way? All I need to do is change a constraint on a existing column and give it a default value.

回答1:

That's one of the better-known drawbacks of SQLite (no MODIFY COLUMN support on ALTER TABLE), but it's on the list of SQL features that SQLite does not implement.

edit: Removed bit that mentioned it may being supported in a future release as the page was updated to indicate that is no longer the case

回答2:

If the modification is not too big (e.g. change the length of a varchar), you can dump the db, manually edit the database definition and import it back again:

echo '.dump' | sqlite3 test.db > test.dump

then open the file with a text editor, search for the definition you want to modify and then:

cat test.dump | sqlite3 new-test.db

回答3:

As said here, these kind of features are not implemented by SQLite.

As a side note, you could make your two first steps with a create table with select:

CREATE TABLE tmp_table AS SELECT id, name FROM src_table

回答4:

When I ran "CREATE TABLE tmp_table AS SELECT id, name FROM src_table", I lost all the column type formatting (e.g., time field turned into a integer field

As initially stated seems like it should be easier, but here is what I did to fix. I had this problem b/c I wanted to change the Not Null field in a column and Sqlite doesnt really help there.

Using the 'SQLite Manager' Firefox addon browser (use what you like). I created the new table by copying the old create statement, made my modification, and executed it. Then to get the data copied over, I just highlighted the rows, R-click 'Copy Row(s) as SQL', replaced "someTable" with my table name, and executed the SQL.