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DB_E_COLUMNUNAVAILABLE
Meaning
Windows documents DB_E_COLUMNUNAVAILABLE as “Requested column is valid, but could not be retrieved. This could be due to a forward only cursor attempting to go backwards in a row”. In this case, a requested column is valid but its value cannot be retrieved in the current access sequence or row state.
Relevant contract
OLE DB distinguishes numeric ordinals, DBID-based column identifiers and per-column status. Metadata from IColumnsInfo or a row object is authoritative for the current result shape; cached identifiers can become invalid after command, schema or projection changes.
Investigation of this result should start with the current command result, rowset or row object and the metadata generation from which the column reference came.
Diagnostic sequence
- Identify the exact failing stage: a requested column is valid but its value cannot be retrieved in the current access sequence or row state.
Conditions that specifically lead to it
- Cause 1: a forward-only row object is asked to revisit an earlier column.
- Cause 2: overlapping IRow::GetColumns calls violate sequential access.
- Cause 3: the provider knows the column but cannot materialize its value in the current state.
Evidence to collect
A useful diagnostic event records provider CLSID and version, process architecture, interface IID and method, object correlation ID, transaction state and the immediately preceding HRESULT. When recording diagnostic data involving column names, row values and query projections, use types, lengths, hashes or redacted identifiers rather than secrets or complete business data.
- Evidence 1: column DBID and requested sequence.
- Evidence 2: prior GetColumns ranges on the same row object.
- Evidence 3: per-column DBCOLUMNACCESS status and provider error records.
Corrective actions
- Action 1: request forward-only columns in monotonic order.
- Action 2: fetch overlapping values in one call when possible.
- Action 3: recreate or refetch the row when earlier data must be revisited.
Retry and recovery
Retry rule: retry only with an access sequence supported by the row object or after obtaining a new row instance.
Difference from nearby HRESULT values
DB_E_NOCOLUMN means the column ID is invalid, while DB_E_COLUMNUNAVAILABLE means the column exists but cannot be retrieved now.
Practical scenario
A reader fetches columns 1 through 3 and then asks again for column 2 on a sequential row; caching the first value avoids it. Keeping it with the method and object state makes this scenario diagnosable instead of reducing it to “database error”.
Official Microsoft references
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