oracle left join 重复

Oracle中的left join可能会导致重复数据。这是因为left join会保留左表中的所有行，而右表中可能会有多个匹配的行。因此，如果左表中的一行与右表中的多个行匹配，则结果集中将包含左表中的该行的多个副本。为避免这种情况，可以使用distinct关键字或使用子查询来过滤重复行。

相关问题

oracle LEFT JOIN

LEFT JOIN 是一种关联查询（JOIN），它返回左表中的所有行和右表中匹配的行。如果右表中没有匹配的行，则返回 NULL 值。Oracle 中使用 LEFT JOIN 的语法如下：

SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

其中，table1 是左表，table2 是右表，ON 是关联条件，如果关联条件成立，则返回左表和右表中匹配的行。如果关联条件不成立，则左表中的所有行都将被返回，右表中匹配的行将被设置为 NULL 值。

Oracle left join

A left join in Oracle is a type of join operation that returns all the records from the left table (also known as the "driving" or "preserved" table) and matching records from the right table, if any exist. If there are no matching records in the right table, the result set will contain NULL values for the right table columns.

The syntax for a left join in Oracle is:

SELECT column1, column2, ...
FROM table1
LEFT JOIN table2
ON table1.column = table2.column;

In this example, the LEFT JOIN statement is used to join table1 and table2 on the specified column. The result set will contain all the records from table1, and matching records from table2, if any exist. If there are no matching records in table2, the result set will contain NULL values for the table2 columns.

The LEFT JOIN statement can also be combined with other clauses, such as WHERE or ORDER BY, to further filter and sort the result set.