Think like the best software engineer and give e the code for :
I have been struggle with this SQL assignment and need some help. The query needs to pull out all time equipment is spent in its "opera

Question

Think like the best software engineer and give e the code for : 
I have been struggle with this SQL assignment and need some help. The query needs to pull out all time equipment is spent in its "operating" state based on shift times. Shifts start on Monday at 
4
am and end on Tuesday 
1
:
3
0
 ﻿am
.
,
 ﻿then start again at 
4
am
,
 ﻿this pattern goes till 
1
:
3
0
am on Friday. Friday
-
Sunday, shifts start at 
4
am and end at 
2
:
3
0
pm each day. Below is the query i have but the problem with it is that the "operating" time that is pulled out for each equipment ID is a very large negative number. For example the "Days
_
in
_
State" column for the "Saw" equipment ID returned 
-
1
2
4
1
5
3
6
7
.
4
4
 ﻿days.
SELECT
﻿ Equipment
_
ID
,
﻿ STATE,
﻿ Equipment
_
DESC,
﻿ SUM
(
ROUND
(
(
COMPLETE
_
DATE 
-
 ﻿START
_
DATE
)
,
2
)
)
 ﻿AS DAYS
_
IN
_
STATE,
﻿ SUM
(
ROUND
(
(
COMPLETE
_
DATE 
-
 ﻿START
_
DATE
)
 
*
 
2
4
,
2
)
)
 ﻿AS HOURS
_
IN
_
STATE
FROM 
(
﻿ SELECT
﻿ A
.
Device
_
id AS Equipment
_
ID
,
﻿ A
.
State,
﻿ A
.
Description AS Equipment
_
DESC,
﻿
﻿ CASE
﻿ WHEN A
.
UPDATED
_
DATE 
>
 ﻿TO
_
DATE
(
'
0
7
-
APR
-
2
5
'
,
 
'
DD
-
MON
-
YY
'
)
﻿ THEN A
.
UPDATED
_
DATE
﻿ ELSE TO
_
DATE

VIPSolutions · Accepted Answer

Absolutely! Let’s walk through your SQL problem step by step, explain the cause of your issue (negative days), and show you a robust solution.

---

## **Step 1: Understanding Your Requirements**

You want to:
- Calculate the total time **each piece of equipment** spends in the **"Operating"** state.
- Only **include times that overlap with "shift" hours** defined as:
  - **Monday 4am – Tuesday 1:30am** (repeat for Tue, Wed, Thu; all shifts start 4am, end next day 1:30am)
  - **Friday–Sunday:** shifts are **4am–2:30pm** **each day**
- Your table: **Equipment_HISTORY**
  - **RECNO** (row id), **Device_id**, **State**, **Description**, **UPDATED_DATE** (when status changed)
- Your query logic: Join each “operating” row to its next row (to determine start/end for each state).

---

## **Step 2: Why Negative Values?**

Negative values in your calculation usually mean:
- **COMPLETE_DATE < START_DATE**
- This happens if your join logic is reversed, or if you mismatch the order of records.
- Also, your WHERE clause logic is off: you use `A.STATE = ANY ('Operating')` and `A.Device_ID = ANY (...)` which is incorrect SQL syntax for Oracle.

---

## **Step 3: How to Fix?**

**Key steps:**
1. **Correct Join**: For each record, get the start and end time of each "Operating" state.
2. **Calculate overlap** of each operating period with the actual "shift" periods.
3. **Sum up the overlapping durations**.

---

## **Step 4: How to Calculate Shift Overlap**

For each "Operating" period, you must compute how much of that period falls **within** the shift times.

- This is a classic “interval overlap” problem.
- For each "Operating" interval and each shift interval, calculate the overlap, and sum.

---

## **Step 5: SQL Approach**

Let’s break it down:

### **A. Get Each “Operating” Period**

```sql
WITH operating_periods AS (
  SELECT
    a.Device_id AS Equipment_ID,
    a.State,
    a.Description AS Equipment_DESC,
    a.UPDATED_DATE AS START_DATE,
    LEAD(a.UPDATED_DATE) OVER (PARTITION BY a.Device_id ORDER BY a.UPDATED_DATE) AS COMPLETE_DATE
  FROM Equipment_HISTORY a
  WHERE a.State = 'Operating'
    AND a.Description NOT LIKE '%Test%'
    AND a.Description NOT LIKE '%Second_Floor%'
    AND a.Device_id IN ('Press', 'Mill', 'Furnace', 'Saw')
)
```
- **LEAD()** gets the next UPDATED_DATE, so each row represents a period in “Operating” state.

---

### **B. Generate Shift Intervals**

We need a table of all possible shift windows during your date range. This is best done with a recursive CTE or a numbers table.

**Let’s assume you have a table called `dates` with one row per day.**

If not, you can create it like this (for Oracle):

```sql
-- Generate all days in your range
WITH dates AS (
  SELECT TO_DATE('07-APR-25','DD-MON-YY') + LEVEL - 1 AS day
  FROM dual
  CONNECT BY LEVEL  s.SHIFT_START
GROUP BY
  op.Equipment_ID, op.State, op.Equipment_DESC
```

- For each overlap, `LEAST(op.COMPLETE_DATE, s.SHIFT_END) - GREATEST(op.START_DATE, s.SHIFT_START)` gives the time in days.
- Multiplying by 24 gives hours.

---

## **Step 6: Full Query**

Here is the **full Oracle SQL** solution, stepwise:

```sql
WITH dates AS (
  SELECT TO_DATE('07-APR-25','DD-MON-YY') + LEVEL - 1 AS day
  FROM dual
  CONNECT BY LEVEL  TO_DATE('07-APR-25','DD-MON-YY'))
)
SELECT
  p.Equipment_ID,
  p.State,
  p.Equipment_DESC,
  ROUND(SUM((LEAST(p.COMPLETE_DATE, s.SHIFT_END) - GREATEST(p.START_DATE, s.SHIFT_START))), 4) AS DAYS_IN_STATE,
  ROUND(SUM((LEAST(p.COMPLETE_DATE, s.SHIFT_END) - GREATEST(p.START_DATE, s.SHIFT_START)) * 24), 2) AS HOURS_IN_STATE
FROM
  periods_in_range p
  JOIN shifts s
    ON p.START_DATE < s.SHIFT_END
   AND p.COMPLETE_DATE > s.SHIFT_START
GROUP BY
  p.Equipment_ID, p.State, p.Equipment_DESC
ORDER BY
  p.Equipment_ID;
```

---

## **Step 7: Conclusion**

- Your negative values came from reversed or mismatched interval logic.
- The robust approach is to **explicitly calculate the overlap between each "Operating" interval and each shift window**.
- Use analytic functions (`LEAD`) to create intervals, a

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