Workaround for deleting Columns in SQLite

Intro :

SQLite has limited ALTER TABLE support that you can use to add a column to the end of a table or to change the name of a table. If you want to make more complex changes in the structure of a table, you will have to recreate the table. You can save existing data to a temporary table, drop the old table, create the new table, then copy the data back in from the temporary table.

From the docs.

It is not possible to rename a column, remove a column, or add or remove constraints from a table.

source : http://www.sqlite.org/lang_altertable.html

While you can always create a new table and then drop the older one.

I will try to explain this this workaround with an example.

sqlite> .schema
CREATE TABLE person(
 id INTEGER PRIMARY KEY, 
 first_name TEXT,
 last_name TEXT, 
 age INTEGER, 
 height INTEGER
);
sqlite> select * from person ; 
id          first_name  last_name   age         height    
----------  ----------  ----------  ----------  ----------
0           john        doe         20          170       
1           foo         bar         25          171  

Now you want to remove the column height from this table.

Create another table called new_person

sqlite> CREATE TABLE new_person(
   ...>  id INTEGER PRIMARY KEY, 
   ...>  first_name TEXT, 
   ...>  last_name TEXT, 
   ...>  age INTEGER 
   ...> ) ; 
sqlite> 

Now copy the data from the old table

sqlite> INSERT INTO new_person
   ...> SELECT id, first_name, last_name, age FROM person ;
sqlite> select * from new_person ;
id          first_name  last_name   age       
----------  ----------  ----------  ----------
0           john        doe         20        
1           foo         bar         25        
sqlite>

Now Drop the person table and rename new_person to person

sqlite> DROP TABLE IF EXISTS person ; 
sqlite> ALTER TABLE new_person RENAME TO person ;
sqlite>

So now if you do a .schema, you will see

sqlite>.schema
CREATE TABLE "person"(
 id INTEGER PRIMARY KEY, 
 first_name TEXT, 
 last_name TEXT, 
 age INTEGER 
);

So that’s how you insert and delete columns from an SQLite Database

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