OracleSQLWHERE 子句中的(+)符号是什么意思？

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Oracle: (+)在 WHERE 子句中做什么

考虑下面简化的 SQL 查询，在 Oracle 数据库环境中(尽管我不确定它是否是 Oracle 特有的) :

SELECT
t0.foo, t1.bar
FROM
FIRST_TABLE t0, SECOND_TABLE t1
WHERE
t0.ID (+) = t1.ID;

WHERE子句中的 (+)表示法是什么？如果这是一个无知的菜鸟问题，我很抱歉，但是在谷歌或 StackOverflow 上搜索 非常很困难... 因为即使使用引号，搜索引擎也会看到一个“ +”符号，似乎想把它当作某种逻辑指令。

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最佳答案

This is an Oracle-specific notation for an outer join. It means that it will include all rows from t1, and use NULLS in the t0 columns if there is no corresponding row in t0.

In standard SQL one would write:

SELECT t0.foo, t1.bar
FROM FIRST_TABLE t0
RIGHT OUTER JOIN SECOND_TABLE t1;

Oracle recommends not to use those joins anymore if your version supports ANSI joins (LEFT/RIGHT JOIN) :

Oracle recommends that you use the FROM clause OUTER JOIN syntax rather than the Oracle join operator. Outer join queries that use the Oracle join operator (+) are subject to the following rules and restrictions […]


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