How Can a SQL Server 2008 Query with an Invalid Column Reference Still Execute Successfully?

SQL Server 2008 Management Studio: Unexpected Query Execution Despite Invalid Syntax

SQL Server 2008 Management Studio sometimes exhibits counter-intuitive behavior regarding syntax errors. A recent case involved a query referencing a non-existent column ("hs_id") within a subquery, yet the query executed without error.

The query's structure is key to understanding this behavior. The outer DELETE statement targets the Photo table, using a subquery to identify rows for deletion. This subquery selects "hs_id" from the HotelSupplier table where "id = 142".

The error lies in the subquery: HotelSupplier lacks a column named "hs_id"; the correct column name is "hs_key". However, the outer query does contain "hs_id" (in the Photo table). This allows SQL Server to resolve the ambiguous "hs_id" reference in the subquery to the "hs_id" column in the Photo table.

Consequently, the subquery returns a set of "hs_id" values based on the Photo table's data, which are then used to filter the DELETE operation. The query's successful execution, despite the initial syntax error, stems from this implicit column resolution.

This behavior, while potentially surprising, isn't inherently problematic. It underscores the critical need for explicit column referencing (using fully qualified names or aliases) to prevent ambiguity and maintain data integrity.

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