This article provides a comprehensive guide to SQL (Structured Query Language), focusing on its fundamental concepts, query operations, and practical applications. It details Data Definition Language (DDL) commands used for structuring databases, including creating and dropping databases and tables. The guide also elaborates on various SQL constraints such as NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK, and DEFAULT, illustrating their implementation through both table creation and alteration statements. AI
RANK_REASON The article is a tutorial or guide on a technical topic, not a research paper or a new model release. [lever_c_demoted from research: ic=1 ai=0.1]
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