How to assign a value under certain conditions by referring to different criteria in a separate table using SQL?

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You can assign a value under certain conditions by joining the table with the criteria table and using a CASE statement to set the value based on the criteria.

Example:

Table A (customers):

| customerid | customername | category | |-------------|---------------|----------| | 1 | John Smith | | | 2 | Mary Johnson | | | 3 | James Brown | |

Table B (criteria):

| category | minimum_sales | |----------|---------------| | A | 10000 | | B | 5000 | | C | 0 |

To assign a category based on minimum sales, you can join the two tables and use a CASE statement to set the category based on the minimum_sales criteria:

SELECT
  customer_id,
  customer_name,
  CASE
    WHEN sales > minimum_sales
    THEN category
    ELSE ''
  END AS category
FROM
  customers
  JOIN criteria ON customers.category = criteria.category

This query will output the following result:

| customerid | customername | category | |-------------|---------------|----------| | 1 | John Smith | C | | 2 | Mary Johnson | A | | 3 | James Brown | B |

In this example, customer John Smith does not meet the minimum sales criteria for category A or B, so the category is set to C. Mary Johnson meets the minimum sales criteria for category A, so that category is assigned. James Brown meets the minimum sales criteria for category B, so that category is assigned.