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title: BC 29 lets a single index span base table and table extension fields
summary: Business Central 29 allows table extension keys to span both base table and extension fields in a single index, eliminating a long-standing constraint. This enables simpler indexing solutions for filtered lists, reporting extractions, and performance problems that previously required architectural workarounds.
tier: community
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tags:
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  - table extensions
  - performance
  - al development
  - database storage
  - bc 29
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    title: BC 29 lets a single index span base table and table extension fields
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    title: BC 29 lets a single index span base table and table extension fields
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    quote: Every index costs writes. An index that makes one list fast makes every insert and modify on that table slower.
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post_id: tag:blogger.com,1999:blog-1492436440038408053.post-483274250682537951
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source_name: Mohana's Dynamics NAV & BC blog
url: http://mohana-dynamicsnav.blogspot.com/2026/09/bc-29-lets-single-index-span-base-table.html
published_at: "2026-09-07T12:50:08.000Z"
author: Mohana Yadav
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words: 1031
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  - text: Every index costs writes. An index that makes one list fast makes every insert and modify on that table slower.
    why_it_matters: Critical caution for developers considering new cross-boundary indexes to avoid unforeseen performance degradation
code_objects_mentioned:
  - table Sales Invoice Header
  - table Item Ledger Entry
  - table G/L Entry
  - table Customer
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# BC 29 lets a single index span base table and table extension fields

[Read the post](http://mohana-dynamicsnav.blogspot.com/2026/09/bc-29-lets-single-index-span-base-table.html) · Mohana's Dynamics NAV & BC blog (Mohana Yadav) · 2026-09-07 · 1031 words · tier community · reviewed (checked by Opus)

> Business Central 29 allows table extension keys to span both base table and extension fields in a single index, eliminating a long-standing constraint. This enables simpler indexing solutions for filtered lists, reporting extractions, and performance problems that previously required architectural workarounds.

## Key points

- Version 29 removes the restriction that keys must contain either all base table fields or all extension fields, but not both
- The change is enabled by storing all AL table fields in the same physical database table instead of separate companion tables
- Cross-boundary keys solve real performance problems like filtering on base table fields while sorting on extension fields
- Developers must still consider the 40-key-per-table limit and write performance costs when adding new indexes
- The capability is in public preview for online sandboxes only; on-premises guidance will follow general availability in October 2026

## Quotes

- "Every index costs writes. An index that makes one list fast makes every insert and modify on that table slower." (Critical caution for developers considering new cross-boundary indexes to avoid unforeseen performance degradation)

## AL objects mentioned

As named in the post. A name that matches one object page by exact type and name links to it; the others stay as named.

- [table 112 "Sales Invoice Header"](../../objects/table/112.md)
- [table 32 "Item Ledger Entry"](../../objects/table/32.md)
- [table 17 "G/L Entry"](../../objects/table/17.md)
- [table 18 "Customer"](../../objects/table/18.md)

## Context

- Features: cross-boundary keys, table extension indexing, mixed-field keys, schema storage consolidation, index optimization
- Versions: 29, 28, 23, 18

Source: Mohana's Dynamics NAV & BC blog, community blog. Summary, key points and quotes are derived (CONTENT-NOTICE.md); read the original for the full text.