How to use pandas.to_sql but only add row if row doesn't exist yet

Question

I have some experience with python but very new to the SQL thing and trying to use pandas.to_sql to add table data into my database, but when I add I want it to check if the data exists before append

This are my 2 dataframes

>>> df0.to_markdown()
|    |   Col1 |   Col2 |
|---:|-------:|-------:|
|  0 |      0 |     00 |
|  1 |      1 |     11 |

>>> df1.to_markdown()
|    |   Col1 |   Col2 |
|---:|-------:|-------:|
|  0 |      0 |     00 |
|  1 |      1 |     11 |
|  2 |      2 |     22 |

So here I use the pandas to_sql

>>> df0.to_sql(con=con, name='test_db', if_exists='append', index=False)
>>> df1.to_sql(con=con, name='test_db', if_exists='append', index=False)

Here I check my data inside the database file

>>> df_out = pd.read_sql("""SELECT * FROM test_db""", con)
>>> df_out.to_markdown()
|    |   Col1 |   Col2 |
|---:|-------:|-------:|
|  0 |      0 |      0 |
|  1 |      1 |     11 |
|  2 |      0 |      0 | # Duplicate
|  3 |      1 |     11 | # Duplicate
|  4 |      2 |     22 | 

But I want my database to look like this, so I don't want to add the duplicate data to my database

|    |   Col1 |   Col2 |
|---:|-------:|-------:|
|  0 |      0 |      0 |
|  1 |      1 |     11 |
|  3 |      2 |     22 | 

Is there any option I can set or some line of code to add to make this happend?

Thankyou!

edit: There are some SQL code to only pull unique data, but what I want to do is don't add the data to the database in the first place

Answer 1

Don't use to_sql a simple query can work

query = text(f""" INSERT INTO test_db VALUES {','.join([str(i) for i in list(df0.to_records(index=False))])} ON CONFLICT ON CONSTRAINT test_db_pkey DO NOTHING""")

self.engine.connect().execute(query)

For each DataFrame change df0 to df1

Follow these link for a better understanding

• Insert values if records don't already exist in Postgres

• How to upsert pandas DataFrame to PostgreSQL table?

Answer 2

For example in my Sqlite 3 database I used temporary table:

I inserted all the dataframe data into temporary table:

df0.to_sql(con=con, name='temptable', if_exists='append', index=False)
df1.to_sql(con=con, name='temptable', if_exists='append', index=False)

Then I copy only new data and drop (delete) the table:

con.executescript('''
INSERT INTO test_db
SELECT test_db.* FROM temptable 
LEFT JOIN test_db on 
   test_db.Col1 = temptable.Col1
WHERE test_db.Col1 IS NULL; -- only items, that not presented in 'test_db' table

DROP TABLE temptable;
''')

Answer 3

add this code to your function

remove_duplicate = 'EXEC remove_duplicate'
cursor.execute(remove_duplicate)
cursor.commit()

and create procedure in your db:

    CREATE PROCEDURE remove_duplicate AS
BEGIN
;WITH duplicates as (SELECT col1, col2,
                    ROW_NUMBER() OVER (PARTITION BY col1, col2, ORDER BY col1) AS number_of_duplicates
    FROM dbo.table)
    DELETE FROM duplicates WHERE number_of_duplicates > 1

END
go