SQL LEFT JOIN: How to Assign 0 to Missing Values in 'num' Column Based on 'DS' Dimension

You can use the COALESCE function to assign a value of 0 to missing 'num' values in a SQL LEFT JOIN operation based on the 'DS' dimension. The COALESCE function returns the first non-NULL value from a list of arguments. Therefore, when the 'num' value is NULL, COALESCE will return 0.

Here's an example query:

SELECT a.DS, COALESCE(b.num, 0) AS num
FROM table_a a 
LEFT JOIN table_b b ON a.DS = b.DS;

This query joins table_a and table_b based on the 'DS' column. The COALESCE function checks if 'num' in table_b is NULL. If it is, it returns 0; otherwise, it returns the actual 'num' value.