GRASS-Wiki - User contributions [en]

Sqlite Drop Column

2009-10-13T10:31:38Z

⚠️Robbiebow:

'''Q:''' How can I drop a column in sqlite-databases?

New '''A:''' GRASS 6.3.cvs contains v.db.dropcol which supports it.

Old '''A:''' It is not possible to drop columns within sqlite using the syntax ALTER TABLE DROP COLUMN [1]. However, there is a workaround for this issue [2]:

<pre>
BEGIN TRANSACTION;
CREATE TEMPORARY TABLE t1_backup(a,b);
INSERT INTO t1_backup SELECT a,b FROM t1;
DROP TABLE t1;
CREATE TABLE t1(a,b);
INSERT INTO t1 SELECT a,b FROM t1_backup;
DROP TABLE t1_backup;
COMMIT;
</pre>

It's obvious that this is a little bit complex. But if you use sqlitebrowser [3] this can be done with a few mouse-clicks (look under -->modify table for a button "remove field". See also the Firefox SQLite Manager add-on [4], which is similar to SqliteBrowser.

Alternatively, you could try this approach, which is slightly fewer steps:

<pre>
BEGIN TRANSACTION;
CREATE TABLE t1_new (
foo TEXT PRIMARY KEY,
bar TEXT,
baz INTEGER
);

INSERT INTO t1_new SELECT foo, bar, baz FROM t1;
DROP TABLE t1;
ALTER TABLE t1_new RENAME TO t1;
COMMIT;
</pre>

* [1] http://www.sqlite.org/omitted.html
* [2] http://www.sqlite.org/faq.html#q11
* [3] http://sqlitebrowser.sourceforge.net/
* [4] https://addons.mozilla.org/en-US/firefox/addon/5817

[[Category:FAQ]]

Sqlite Drop Column

2009-10-13T10:30:57Z

⚠️Robbiebow:

'''Q:''' How can I drop a column in sqlite-databases?

New '''A:''' GRASS 6.3.cvs contains v.db.dropcol which supports it.

Old '''A:''' It is not possible to drop columns within sqlite using the syntax ALTER TABLE DROP COLUMN [1]. However, there is a workaround for this issue [2]:

<pre>
BEGIN TRANSACTION;
CREATE TEMPORARY TABLE t1_backup(a,b);
INSERT INTO t1_backup SELECT a,b FROM t1;
DROP TABLE t1;
CREATE TABLE t1(a,b);
INSERT INTO t1 SELECT a,b FROM t1_backup;
DROP TABLE t1_backup;
COMMIT;
</pre>

It's obvious that this is a little bit complex. But if you use sqlitebrowser [3] this can be done with a few mouse-clicks (look under -->modify table for a button "remove field". See also the Firefox SQLite Manager add-on [4], which is similar to SqliteBrowser.

Alternatively, you could try this approach, which is slightly fewer steps:

<pre>
BEGIN TRANSACTION;
CREATE TABLE t1_new (
foo TEXT PRIMARY KEY,
bar TEXT,
baz INTEGER,
);

INSERT INTO t1_new SELECT foo, bar, baz FROM t1;
DROP TABLE t1;
ALTER TABLE t1_new RENAME TO t1;
COMMIT;
</pre>

* [1] http://www.sqlite.org/omitted.html
* [2] http://www.sqlite.org/faq.html#q11
* [3] http://sqlitebrowser.sourceforge.net/
* [4] https://addons.mozilla.org/en-US/firefox/addon/5817

[[Category:FAQ]]