Thank you for your query. I understand that you want to execute a SQL query on Redshift and the result of that query should be in JSON format. Please correct me if I have misunderstood your query.

In Redshift there is not out of the box function which could convert SQL output into a JSON payload, however this could be achieved using other Redshift functions. Please find below an example SQL query :

SELECT '[' || LISTAGG( '{' || '"login":"' || CAST(login AS VARCHAR) || '",' || '"tue_sat":"' || CAST(tue_sat AS VARCHAR) || '",' || '"shift_start":"' || CAST(shift_start AS VARCHAR) || '"' || '}' , ',') WITHIN GROUP (ORDER BY login) || ']' AS json_output FROM historical_rota

In this example, the columns are cast to VARCHAR and concatenated into a JSON string using string concatenation operators (||) and the appropriate JSON syntax. The LISTAGG function is used to concatenate the JSON strings into a JSON array.

If any of the columns have a NULL value, the resulting JSON output will contain a null value for that key. However, you can modify the query to handle NULL values by using the COALESCE function to replace NULL values with a default value (such as an empty string). Here's an example query that uses COALESCE: SELECT '[' || LISTAGG( '{' || '"login":' || CASE WHEN login IS NULL THEN 'null' ELSE '"' || CAST(login AS VARCHAR) || '"' END || ',"tue_sat":' || CASE WHEN tue_sat IS NULL THEN 'null' ELSE '"' || CAST(tue_sat AS VARCHAR) || '"' END || ',"shift_start":' || CASE WHEN shift_start IS NULL THEN 'null' ELSE '"' || CAST(shift_start AS VARCHAR) || '"' END || '}'
, ',') WITHIN GROUP (ORDER BY login) || ']' AS json_output FROM historical_rota

In this example, the COALESCE function is used to replace any NULL values with an empty string (''). This ensures that the resulting JSON output will not contain any null values for these columns.

Additional References: [+] https://docs.aws.amazon.com/redshift/latest/dg/r_LISTAGG.html [+] https://docs.aws.amazon.com/redshift/latest/dg/r_CASE_function.html [+] https://docs.aws.amazon.com/redshift/latest/dg/json-functions.html

Redshift table data could also be outputed as a JSON payload through use of a Programatic Redshift Data API call using Python library 'psycopg2'.

This could be achieved by performing the steps below.

1. Connect to your Redshift cluster using psycopg2-binary Python library
2. Execute a SQL query to select data from a table. You then fetch all the rows from the table and loop through them to create a dictionary for each row.
3. The dictionary keys correspond to the column names, and the values correspond to the column values in the row.
4. You add each row dictionary to a list to create a list of JSON objects. Finally, you convert the list of JSON objects to a JSON string using the json.dumps() method and print it.

Please find below a sample Pyhon program which achieves the above defined use-case.

SCRIPT START

import json import psycopg2

Connect to your Redshift cluster using psycopg2

conn = psycopg2.connect( host='your-redshift-cluster-endpoint', port=5439, dbname='your-database-name', user='your-username', password='your-password' )

Create a cursor object to execute SQL queries

cur = conn.cursor()

Execute a SQL query to select data from a table

cur.execute("SELECT * FROM your_table")

Fetch all rows from the table

rows = cur.fetchall()

Define an empty list to store JSON objects

json_payload = []

Loop through the rows and create a JSON object for each row

for row in rows: # Create a dictionary to store the row data row_dict = {} row_dict['column1_name'] = row[0] row_dict['column2_name'] = row[1] row_dict['column3_name'] = row[2] # Add the row dictionary to the JSON payload list json_payload.append(row_dict)

Convert the JSON payload list to a JSON string

json_string = json.dumps(json_payload)

Print the JSON string

print(json_string)

SCRIPT END