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。

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oracle left join

在Oracle中，LEFT JOIN是一种连接操作，它用于将两个表的数据合并在一起，同时显示左表的所有数据和与之关联的右表数据。左表是基础表，它的所有数据都会被显示出来，而右表只会显示能与左表关联上的数据。 这种连接操作可以使用关键字LEFT JOIN或者将LEFT JOIN写在B表的后面。这种连接操作可以帮助我们获取左表和右表的相关数据，而不会丢失左表的任何数据。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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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.