Answers for "alter table if not exists column"

add column if not exists

ALTER TABLE test ADD COLUMN IF NOT EXISTS column_a VARCHAR(255);
ALTER TABLE test MODIFY IF EXISTS column_a VARCHAR(255);

how to check if a column exists before alter the table

conn = sqlite3.connect(':memory:')
c = conn.cursor()
try:
    c.execute('ALTER TABLE mytable ADD COLUMN newcolumn;')
except:
    pass # handle the error
c.close()