Using LIKE query in HAVING Clause

I need to build a query where I will have a clause like the following

SELECT *
FROM tableA 
LEFT JOIN tableB
LEFT JOIN tableC
WHERE tableA.active = 1
HAVING tableC.columnA LIKE '%$search_term%';

1. How can I do this using the query builder?
   
2. How can I ensure that the query is protected from SQL injection?
   

Thanks.

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