数据库的表由什么组成和构成的

网站编辑2023-06-16 14:07:43157

关系数据库是一种以表(或其他形式的数据存储)为基础的数据库系统。它由关系数据定义语言(SQL)和关系运算符(OR)定义的。

SQL 的主要部分是 SQL 命令,它可以让用户使用关系代数来查询、修改和删除表。SQL 命令可以使用多种方式,如:

--- SELECT * FROM table1 --- WHERE table2 IN (SELECT FROM table1 WHERE table2 IN (SELECT FROM table2 WHERE table3 IN (SELECT FROM table3 WHERE table4 IN (SELECT FROM table4 WHERE table5 IN (SELECT FROM table5 WHERE table9 IN (SELECT FROM table9 WHERE table10 IN (SELECT FROM table10 WHERE table1 OR (SELECT FROM table1 OR (SELECT FROM table1 OR SELECT FROM table11 OR SELECT FROM table11 OR SELECT FROM table13 OR