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 a table

• column_names (str or list or None) – (list of) column name(s); when column_names=None (default), all available columns are included

• schema_name (str) – name of a schema

Examples:

>>> from pyhelpers.dbms import PostgreSQL
>>> from pyhelpers._cache import example_dataframe

>>> testdb = PostgreSQL('localhost', 5432, 'postgres', database_name='testdb')
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'}

Fig. 15 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)

Fig. 16 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.