ViewInvdtlTaxPer

### 1. Overview
 `ViewInvdtlTaxPer` is a summary view providing the applicable GST percentages (CGST, SGST, IGST) at the invoice level. It aggregates tax rates typically found in line-item details into a single row per invoice header.
 
 ### 2. Grain & Lifecycle
 **Grain:** One row per Invoice (`compcode`, `invno`, `invyear`).
 **Lifecycle:** Data is generated or updated when an invoice is finalized or tax calculations are performed on invoice line items.
 
 ### 3. Column Dictionary
 | Column | Type | Nullable | Meaning | Allowed Values | SQL Usage |
 | :--- | :--- | :--- | :--- | :--- | :--- |
 | index | integer | No | Primary Key / Row identifier | | Internal reference |
 | compcode | string | No | Company identifier | e.g., 'DAS' | Join key |
 | invno | integer | No | Invoice number | | Join key |
 | invyear | integer | No | Financial year of invoice | e.g., 2013 | Join key |
 | cgst_per | string | Yes | Central GST rate percentage | e.g., '9.00' | Reporting/Display |
 | sgst_per | string | Yes | State GST rate percentage | e.g., '9.00' | Reporting/Display |
 | igst_per | string | Yes | Integrated GST rate percentage | e.g., '18.00' | Reporting/Display |
 
 ### 4. Relationships & Join Map
 #### Confirmed Joins
 - **invhdr**: Join on `(compcode, invno, invyear)` to access invoice dates, customer codes, and total amounts.
 
 #### Likely Joins
 - **oahdr**: (Likely) Join via `invhdr` on `(compcode, oa_no)` to link tax rates back to the original Order Advice.
 
 ### 5. Metadata Joins
 | Metadata Table | JOIN ON | When to Use | Columns Added |
 | :--- | :--- | :--- | :--- |
 | `invhdr` | `compcode, invno, invyear` | To filter by date, customer, or cancellation status. | `invdate`, `custcode`, `cancel_flag` |
 | `statemas` | `compcode, statecode` (via `invhdr`) | To validate tax rates against specific state GST compliance. | `statename`, `gst_state_code` |
 
 ### 6. Query Patterns & Performance Notes
 - **Filtering:** Always filter by `compcode` and `invyear` first to leverage indexing on the underlying invoice tables.
 - **Data Type Note:** Tax percentages are stored as strings. Cast to `DECIMAL` or `FLOAT` for arithmetic operations.
 - **Null Handling:** `NULL` values in tax columns indicate that specific tax type was not applied to the invoice.
 
 ### 7. Example Queries
 
 -- 1. Get GST rates for a specific invoice
 SELECT cgst_per, sgst_per, igst_per
 FROM ViewInvdtlTaxPer
 WHERE compcode = 'DAS' AND invno = 2349 AND invyear = 2013;
 
 -- 2. Identify invoices with IGST applied (Inter-state sales)
 SELECT invno, invyear, igst_per
 FROM ViewInvdtlTaxPer
 WHERE igst_per IS NOT NULL AND igst_per <> '0';
 
 -- 3. Join with Invoice Header to see tax rates for a specific customer
 SELECT h.invno, h.invdate, t.cgst_per, t.sgst_per
 FROM ViewInvdtlTaxPer t
 JOIN invhdr h ON t.compcode = h.compcode AND t.invno = h.invno AND t.invyear = h.invyear
 WHERE h.custcode = 'C001' AND h.cancel_flag = 'N';
 
 -- 4. List distinct GST combinations used in a financial year
 SELECT DISTINCT cgst_per, sgst_per, igst_per
 FROM ViewInvdtlTaxPer
 WHERE compcode = 'DAS' AND invyear = 2023;
 
 ### SUMMARY_START ### {"one_line_description": "Summary view of CGST, SGST, and IGST percentages applied at the invoice level.", "grain": "One row per invoice (compcode, invno, invyear).", "potential_joins": "invhdr, statemas", "key_columns": "compcode, invno, invyear, cgst_per, sgst_per, igst_per"} ### SUMMARY_END ###

-- Retrieve tax percentage details for a specific invoice (No. 2621) from the year 2013
 SELECT 
  t.compcode, 
  t.invno, 
  t.invyear, 
  t.cgst_per, 
  t.sgst_per, 
  t.igst_per
 FROM ViewInvdtlTaxPer AS t
 WHERE t.compcode = 'DAS' 
  AND t.invno = 2621 
  AND t.invyear = 2013;
 
 -- Join with invoice header to find tax percentages for active invoices belonging to customer 'HML(D)'
 SELECT 
  h.invdate, 
  h.custcode, 
  h.pono, 
  t.cgst_per, 
  t.sgst_per, 
  t.igst_per
 FROM ViewInvdtlTaxPer AS t
 INNER JOIN invhdr AS h 
  ON t.compcode = h.compcode 
  AND t.invno = h.invno 
  AND t.invyear = h.invyear
 WHERE h.compcode = 'DAS' 
  AND h.custcode = 'HML(D)' 
  AND h.cancel_flag = 'N';
 
 -- Aggregate count of tax records grouped by invoice year for company 'DAS'
 SELECT 
  t.invyear, 
  COUNT(t.invno) AS total_invoice_lines
 FROM ViewInvdtlTaxPer AS t
 WHERE t.compcode = 'DAS'
 GROUP BY t.invyear
 ORDER BY t.invyear DESC;
 
 -- Multiple join with invoice header and invoice type master to categorize taxes for specific invoice types
 SELECT 
  h.invno, 
  h.invyear, 
  h.invdate, 
  h.invtype, 
  t.cgst_per, 
  t.sgst_per, 
  t.igst_per
 FROM ViewInvdtlTaxPer AS t
 INNER JOIN invhdr AS h 
  ON t.compcode = h.compcode 
  AND t.invno = h.invno 
  AND t.invyear = h.invyear
 INNER JOIN invtype AS it 
  ON h.compcode = it.compcode 
  AND h.invtype = it.invtype
 WHERE t.compcode = 'DAS' 
  AND h.invtype = 0 
  AND h.invyear = 2018;