merge_on_column_and_more.txt

#Left merge on column StockCode
pd.merge(d4, d5, on='StockCode', how='left')

#Left merge on column Description
pd.merge(d4, d5, on='Description', how='left')

#Left merge on multiple columns
pd.merge(d4, d5, on=['StockCode', 'Description'], how='left')

#The above line of code is the same as:
pd.merge(d4, d5, how='left')

#Distinguishing between data frames even when merging on multiple columns
d4 = pd.DataFrame(df, columns=['InvoiceNo', 'StockCode', 'Description', 'UnitPrice'])[0:11]
d5 = pd.DataFrame(df, columns=['StockCode', 'Description', 'Quantity', 'UnitPrice'])[10:20]
pd.merge(d4, d5, on=['StockCode', 'Description'], how='left')

#You want every column to distuinguish between the two data frames
pd.merge(d4, d5, left_index = True, right_index=True, how='outer')