AL DEVELOPMENT · QUERIES

Business Central Queries in AL: Complete Practical Guide

Query objects provide a structured way to retrieve related Business Central data. This guide explains query structure, dataitems, columns, links, filters, aggregation, Query variables and practical performance considerations.

1. What is a Query in Business Central?

A Query object defines how Business Central data is read from one or more tables. Queries are useful when you need a structured dataset for reporting, integrations or application logic.

2. Basic Query structure

query 50100 "Customer Sales Query" { elements { dataitem(Customer; Customer) { column(CustomerNo; "No.") { } column(CustomerName; Name) { } } } }

3. Multiple dataitems

Queries can combine related dataitems. The relationship between dataitems should reflect the business data you actually need.

dataitem(Customer; Customer) { column(No; "No.") { } dataitem(SalesHeader; "Sales Header") { DataItemLink = "Sell-to Customer No." = Customer."No."; column(DocumentNo; "No.") { } } }

4. Filters and links

Use filters and dataitem links to restrict the dataset. A smaller, purposeful result set is generally easier to process than retrieving unnecessary records and filtering them later.

5. Aggregation

Queries can be used for summarized datasets where grouping and aggregation are appropriate. Always verify that the resulting dataset matches the business requirement.

6. Query variables in AL

MyQuery.Open(); while MyQuery.Read() do begin // Process returned columns end; MyQuery.Close();

Use the generated query columns through the query variable after opening the query.

7. Query vs Record

Query	Record
Designed for structured multi-table result sets	Designed for working with records and business logic
Useful for read-oriented datasets	Useful for validation, modification and record operations

8. Performance tips

Return only columns you need.
Apply meaningful filters.
Avoid unnecessarily large result sets.
Test with realistic data volumes.
Choose Query or Record based on the actual business operation.

9. Common mistakes

Creating unnecessarily broad queries.
Incorrect dataitem links.
Assuming a query automatically replaces all record-based business logic.
Ignoring the size of the returned dataset.

10. Interview questions

What is a Query object?
What is a dataitem?
How do DataItemLink and filters differ?
When would you use a Query instead of a Record variable?
How can you improve query performance?

Conclusion

Queries are a useful AL tool for structured data retrieval. Good query design starts with a precise dataset, correct relationships, appropriate filters and realistic performance testing.