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本文介绍了SQL中的Cross Join和Cross Apply。Cross Join在无WHERE子句时产生笛卡尔积，带有WHERE子句则类似INNER JOIN。而Cross Apply允许右操作数引用左操作数的列，常用于将表中的值传递给函数，特别是在查询涉及复杂结构如产品BOM时非常有用。
What is Cross Join in SQL?
The SQL CROSS JOIN produces a result set which is the number of rows in the first table multiplied by the number of rows in the second table if no WHERE clause is used along with CROSS JOIN. This kind of result is called as Cartesian Product.
If WHERE clause is used with CROSS JOIN, it functions like an INNER JOIN.
An alternative way of achieving the same result is to use column names separated by commas after SELECT and mentioning the table names involved, after a FROM clause.
Syntax
SELECT *
FROM table1
CROSS JOIN table2;
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