PostgreSQL.null_text_to_empty_string

PostgreSQL.null_text_to_empty_string(table_name, column_names=None, schema_name=None)

Convert null values (in text columns) to empty strings.

Parameters:

• table_name (str) – Name of the table.

• column_names (str | list | None) – (List of) column name(s) to convert null values to empty strings; if column_names=None (default), all available columns are included.

• schema_name (str | None) – Name of the schema; defaults to None.

Examples:

>>> from pyhelpers.dbms import PostgreSQL
>>> from pyhelpers._cache import example_dataframe
>>> testdb = PostgreSQL(database_name='testdb', verbose=True)
Password (postgres@localhost:5432): ***
Creating a database: "testdb" ... Done.
Connecting postgres:***@localhost:5432/testdb ... Successfully.
>>> dat = example_dataframe()
>>> dat['Longitude'] = dat['Longitude'].astype(str)
>>> dat.loc['London', 'Longitude'] = None
>>> dat
             Longitude   Latitude
City
London            None  51.507322
Birmingham  -1.9026911  52.479699
Manchester  -2.2451148  53.479489
Leeds       -1.5437941  53.797418
>>> tbl_name = 'test_table'
>>> testdb.import_data(data=dat, table_name=tbl_name, index=True, verbose=True)
To import data into "public"."test_table" at postgres:***@localhost:5432/postgres
? [No]|Yes: yes
>>> testdb.table_exists(table_name=tbl_name)
True
>>> testdb.get_column_dtype(table_name=tbl_name)
{'City': 'text', 'Longitude': 'text', 'Latitude': 'double precision'}
>>> dat_ = testdb.read_table(tbl_name)
>>> dat_.loc[0, 'Longitude'] is None
True

Figure 20 The table “test_table” in the database “testdb”.

>>> # Replace the 'null' value with an empty string
>>> testdb.null_text_to_empty_string(table_name=tbl_name)
>>> dat_ = testdb.read_table(tbl_name)
>>> dat_.loc[0, 'Longitude']
''

Figure 21 The table “test_table” in the database “testdb” (after converting ‘null’ to empty string).

>>> # Delete the database "testdb"
>>> testdb.drop_database(verbose=True)
To drop the database "testdb" from postgres:***@localhost:5432
? [No]|Yes: yes
Dropping "testdb" ... Done.