compare the schema of two delta tables

Question

Need suggestions on how to compare the schema of two delta tables X and Y. Table Y has N more columns than X. How do I dynamically identify the extra columns and add to table X?

In databricks/python Thanks in advance

Answer 1

You can achieve it with something like this:

def add_missing_columns(df1, df2):
  additional_cols = [F.lit(None).cast(field.dataType).alias(field.name) 
                     for field in df2.schema.fields if field.name not in df1.columns]
  return df1.select("*", *additional_cols)

Usage:

df1 = spark.createDataFrame([('1',), ('2',)], ["col1"])
df2 = spark.createDataFrame([('{1',1, 0.5)], ["col1", "col2", "col3"])
add_missing_columns(df1, df2).show()

+----+----+----+
|col1|col2|col3|
+----+----+----+
|   1|null|null|
|   2|null|null|
+----+----+----+

How it works - it iterates over the columns of 2nd dataframe, and check if it's already in the first dataframe or not. If it's not, it creates a new column with null value, but casted to correct data type.