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Overview

A NULL value indicates that the value does not exist in the database. In Oxla, you can use the NULL option in the COPY TO state to specify a string that will replace NULL values ​​when copying data from the table to a CSV file.

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Syntax

The syntax for using the NULL option in the COPY TO is as follows: 
COPY table_name TO 'file_path' (NULL 'replacement_string');
Parameters in the syntax include:
  • table_name: The table containing the data to be exported.
  • file_path: A CSV file location where the data will be saved.
  • NULL ‘replacement_string': The specified string that will replace NULL values in the exported CSV file. The default value is ' '.

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Example

  1. Create a table with a NULL value.
CREATE TABLE example_table (
  id serial,
  name varchar(50),
  age int,
  city varchar(50)
);

INSERT INTO example_table (name, age, city) VALUES
  ('John', 25, 'New York'),
  ('Alice', NULL, 'Chicago'),
  ('Bob', 30, NULL);
  1. Now, let’s use COPY TO with an empty string:
COPY example_table TO '/path/to/exampleexport.csv' (NULL '');
  1. The NULL values in the table are replaced with the empty string in the CSV file.
1,John,25,"New York"
2,Alice,null,"Chicago"
3,Bob,30,""
You can specify another string to replace the null value, such as blank, empty, invalid, etc.