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To create a Teradata SQL query with a case condition that checks the ID and its starting date, follow these steps:

1. Start by writing the basic SQL statement that selects the desired columns from the appropriate tables. For example:

SELECT column1, column2, column3 FROM table1 JOIN table2 ON table1.ID = table2.ID WHERE ...

1. Add a CASE statement to the SELECT clause. This will allow you to evaluate a condition and return different values based on the result. The syntax for a basic CASE statement is:

CASE WHEN condition THEN value1 WHEN condition THEN value2 ELSE value3 END

1. Add the condition to the CASE statement. In this case, you want to check the ID and its starting date, so you'll need to reference those columns in your condition. For example:

CASE WHEN table1.ID = 12345 AND table1.start_date >= '2021-01-01' THEN 'Active' ELSE 'Inactive' END as status

1. Incorporate the CASE statement into your overall SQL statement. This might involve using it in a WHERE or HAVING clause, or simply including it as a new column in your SELECT statement. For example:

SELECT column1, column2, column3, CASE WHEN table1.ID = 12345 AND table1.start_date >= '2021-01-01' THEN 'Active' ELSE 'Inactive' END as status FROM table1 JOIN table2 ON table1.ID = table2.ID WHERE ...

1. Test and refine your query as needed to ensure it returns the desired results.