在Oracle SQL Developer中简化SQL Select语句

Question

The problem I'm facing right now is I'm working with a SQL query that has over 200 lines of code and at the moment in multiple cases I'm just repeating the same sub-query multiple times in this select statement. In the code below I'm using two of the select statements a lot "avail_qty" and "pct_avail" which both having equations in them. Inside the LOW_CNT_&% SELECT statement I use both of the previous two SELECT statements over and over (this is just one example in my code). I would like to be able to make the equation once and assign it to a variable. Is there any way of doing this? I have tried using the WITH clause but for that you need to use a FROM clause, my FROM clause is massive and would look just as ugly if I were to use a WITH clause (plus instead of repeating the SELECT statement now I would be just repeating the FROM statement).

The reason I don't want to type out the whole equation multiple times is for a two reasons the first is it makes the code easier to read. My other reason is because multiple people edit this query and if someone else were to edit the equation in one spot but forgets to edit it in another spot, that could be bad. Also it doesn't feel like good code etiquette to repeat code over and over.

SELECT 
    all_nbr.total_qty,
    NVL (avail_nbr.avail_qty, 0) AS avail_qty,
    100 * TRUNC ( (NVL (avail_nbr.avail_qty, 0) / all_nbr.total_qty), 2) AS pct_avail,

    CASE
        WHEN ((NVL (avail_nbr.avail_qty, 0)) < 35) 
        THEN CASE
                WHEN ((100 * TRUNC ( (NVL (avail_nbr.avail_qty, 0) / all_nbr.total_qty), 2)) < 35)
                THEN (35 - (NVL (avail_nbr.avail_qty, 0)))
                ELSE 0
             END
        ELSE 0
    END AS "LOW_CNT_&%"
FROM
...

Any help would be awesome!!

Answer 1

If the subquery is exactly the same one, you can pre-compute it as a Common Table Expression (CTE). For example:

with
cte1 as (
  select ... -- long, tedious, repetitive SELECT here
),
cte2 as (
  select ... -- you can reference/use cte1 here
)
select ...
  from cte1 -- you can use cte1 here, multiple times if you want
  join cte2 -- you can also reference/use cte2 here, also multiple times
  join ... -- all other joins

cte1 (you can use any name) is a precomputed table expression that can be used multiple times. You can also have multiple CTEs, each one with different names; also each CTE can reference previous ones.

Answer 2

I have tried using the WITH clause but for that you need to use a FROM clause, my FROM clause is massive and would look just as ugly if I were to use a WITH clause (plus instead of repeating the SELECT statement now I would be just repeating the FROM statement).

You shouldn't need to repeat the from clause. You move all of the query, including that clause, into the CTE; you just pull out the bits that rely on earlier calculations into the main query, which avoids the code repetition.

The structure would be something like:

WITH cte AS (
    SELECT 
        all_nbr.total_qty,
        NVL (avail_nbr.avail_qty, 0) AS avail_qty,
        100 * TRUNC ( (NVL (avail_nbr.avail_qty, 0) / all_nbr.total_qty), 2) AS pct_avail,
    FROM
    ...
)
SELECT
    cte.total_qty,
    cte.avail_qty,
    cte.pct_avail,
    CASE
        WHEN cte.avail_qty, 0 < 35 
        THEN CASE
                WHEN cte.total_qty < 35
                THEN 35 - cte.avail_qty
                ELSE 0
             END
        ELSE 0
    END AS "LOW_CNT_&%"
FROM
    cte;

Your main query only need to refer to the CTE (again, based on what you've shown), and can (only) refer to the prjoection of the CTE, incuding the calculated columns. It can't see the underlying tables, but shouldn't need to.

Or with an inline view instead, the principal is the same:

SELECT
    total_qty,
    avail_qty,
    pct_avail,
    CASE
        WHEN avail_qty < 35
        THEN CASE
                WHEN total_qty < 35
                THEN 35 - avail_qty
                ELSE 0
             END
        ELSE 0
    END AS "LOW_CNT_&%"
FROM
(
    SELECT 
        all_nbr.total_qty,
        NVL (avail_nbr.avail_qty, 0) AS avail_qty,
        100 * TRUNC ( (NVL (avail_nbr.avail_qty, 0) / all_nbr.total_qty), 2) AS pct_avail,
    FROM
    ...
);