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Performance Regression After a SQL Server Upgrade: First Aid

A performance regression after an upgrade hurts most when users are waiting. This post shows a first-aid switch that brings back the old row estimates without lowering the compatibility level, and proves with a demo what changes and what stays. It also covers the undo, the per-query options and the steps that find the real cause.

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Create Table From Another Table: What SELECT INTO Copies

To create table from another table in SQL Server, use SELECT INTO with WHERE 1 = 2 or TOP (0) for the structure alone. This post builds a demo table and compares it with its copy column by column. It shows the identity trap, the computed column that becomes plain, and the statements that add keys, defaults and indexes back.

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