How do you decide the column order in a composite database index for an API query?

Composite indexes and column order

Explains composite index column order with practical .NET data-access examples and production trade-offs.

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A composite index contains more than one column, and the order matters because the database can use the leading columns most effectively. I design it around the query's filter and sort pattern. For example, if most queries filter by tenant and status and sort by created date, the index should reflect that access path.

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Understanding of composite index column order, EF Core/SQL behavior, API boundaries, production risks, and practical debugging or design judgment.

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Explain composite index column order with practical .NET data-access examples and production trade-offs. It matters in real backend work because query shape, indexes, transactions, locking, and data volume can turn harmless-looking code into a production bottleneck. The practical angle is composite index column order, EF Core/SQL behavior, API boundaries, production risks, and practical debugging or design judgment, tied to a concrete production decision.
A composite index contains more than one column, and the order matters because the database can use the leading columns most effectively. I design it around the query's filter and sort pattern. For example, if most queries filter by tenant and status and sort by created date, the index should reflect that access path.
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For WHERE TenantId = @tenant AND Status = @status ORDER BY CreatedAt DESC, an index starting with tenant and status may help because those are equality filters. Then can support ordering. The trade-off is that the same index may not help a query filtering only by , because it does not use the leading columns. I verify with execution plans.

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Treating composite index column order as a syntax detail instead of a production behavior.
Not checking generated SQL, query plans, or actual data volume.
Testing only with tiny local data and assuming production will behave the same.
Fixing symptoms with caching, timeouts, or retries before understanding the data-access cause.

How do you decide the column order in a composite database index for an API query?

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