How to enforce conditions in Common Table Expressions - mysql

Question

We have numerous complex functions that return lists based on passed JSON filter settings. The problem is, MySQL appears (using EXPLAIN) to execute the SQL within a SELECT statement even if a flag is set as false. I'm not sure how to get around this. For example:
WITH cte1 AS
(
SELECT pm.ID
FROM person_main pm
),
cte2 AS
(
SELECT IF
(
#p_filter_job_state_array IS NULL,
(
SELECT NULL
),
(
SELECT sis.ID
FROM cte1 sis
INNER JOIN external_link el ON el.ref_id = sis.ID
WHERE el.headline_value LIKE '%test%'
)
) AS ID
)
SELECT * FROM cte2;
Even though #p_filter_job_state_array is NULL, the engine is still executing the SELECT joining external_link. We have dozens of "frontloading" CTEs that do this, and as the number of filters grow, the execution time is doubling and tripling even though we have no filters set (because the engine is executing the SELECT statements when I thought it was ignoring them based on NULL values). I need to figure out how to write a single query using CTEs and instruct the compiler to avoid executing CTE SELECT statements based on variable settings... is this possible, and if so, how can I do it?
Another example of why this is important is because we do a LOT of frontloading and filtering, and sometimes the caller just wants an array of indexes rather than the entire structure, so we have something like this:
SELECT IF
(
p_array_only,
(
SELECT JSON_ARRAYAGG(jm.ID)
FROM
(
SELECT fs.ID
FROM final_sort fs
LIMIT var_offset, var_rowcount
) jm
),
(
SELECT JSON_OBJECT
(
'data',
(
SELECT JSON_ARRAYAGG(JSON_OBJECT
(
'data_main', get_json_data_main_list(jm.ID)
))
FROM
(
SELECT fs.ID
FROM final_sort fs
LIMIT var_offset, var_rowcount
) jm
)
)
)
)
Of course the issue is if they just want the array, MySQL still executes the other portion of the code. Yes, I could break this into two separate SQL statements, but they use 100% of the same "frontloading" of the code, so it would be inefficient. But this is the main problem; we have a very specific set of filters we need to process, but we also need to skip filters and focus on outputting different structures based on variable settings.

Answer 1

Unfortunately, there wasn't any response from the community; Prepared Statements are probably the best solution (and work fine), but as many know, it turns managing complex code into spaghetti, which can be very frustrating. But it's fast.