SQL data types specify the kind of value a column holds, dictating physical byte storage, validation constraints, and indexing behavior. Key Sub-topics: • Sub-topic 1: Unicode storage trade-offs: VARCHAR (1 byte/char) vs NVARCHAR (2 bytes/char) and memory grant overhead • Sub-topic 2: Precision and scale: DECIMAL(18,2) vs FLOAT rounding bugs and modern DATETIME2 vs legacy DATETIME
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