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问题		答案
Ensures that a column cannot have a NULL value 开始学习		NOT NULL
Ensures that all values in a column are different 开始学习		UNIQUE
A combination of a NOT NULL and UNIQUE. Uniquely identifies each row in a table 开始学习		PRIMARY KEY [MySQL:] UserId auto_increment primary key
Uniquely identifies a row/record in another table 开始学习		FOREIGN KEY
Ensures that all values in a column satisfies a specific condition 开始学习		CHECK
Sets a default value for a column when no value is specified 开始学习		DEFAULT
Used to create and retrieve data from the database very quickly 开始学习		INDEX
It's like a declaration of default value that increments by 1 for each record. 开始学习		auto_increment SQLite: autoincrement

SQL – Constraints