通过自我加入更新

Question

我想更新一个表以指示某些行是其他父项，因此我在该表中添加了“parentid”列。以下查询查找所有的家长：

SELECT ca1.id, ca2.id 
FROM contactassociations ca1 
JOIN contactassociations ca2 ON (ca1.contactid = ca2.contactid) 
where ca1.entitytable = 'EMPLOYER' AND 
ca2.entitytable = 'CLIENT'; 

但是当我尝试去适应这种语法做了更新，这是行不通的：

UPDATE contactassociations ca1 
SET ca1.parentid = ca2.id 
JOIN contactassociations ca2 ON (ca1.contactid = ca2.contactid) 
WHERE ca1.entitytable = 'EMPLOYER' AND ca2.entitytable = 'CLIENT'; 

我得到：

Error starting at line 6 in command: 
UPDATE contactassociations ca1 
SET ca1.parentid = ca2.id 
JOIN contactassociations ca2 ON (ca1.contactid = ca2.contactid) 
WHERE ca1.entitytable = 'EMPLOYER' AND ca2.entitytable = 'CLIENT' 
Error at Command Line:7 Column:28 
Error report: 
SQL Error: ORA-00933: SQL command not properly ended 
00933. 00000 - "SQL command not properly ended" 
*Cause:  
*Action: 

请注意，第7行第28列是“SET”行的结尾。

Answer 1

Oracle不支持在UPDATE语句中的JOIN子句。

使用此：

MERGE 
INTO contactassociations ca1 
USING contactassociations ca2 
ON  (
     ca1.contactid = ca2.contactid 
     AND ca1.entitytable = 'EMPLOYER' 
     AND ca2.entitytable = 'CLIENT' 
     ) 
WHEN MATCHED THEN 
UPDATE 
SET  parentid = ca2.id 

Answer 2

我找到以下样式简单的阅读，但你需要使用别名的UPDATE关键字后面，而不是表名：

UPDATE ca1 
SET ca1.parentid = ca2.id 
FROM contactassociations ca1 
LEFT JOIN contactassociations ca2 ON (ca1.contactid = ca2.contactid) 
WHERE ca1.entitytable = 'EMPLOYER' AND ca2.entitytable = 'CLIENT' 

Answer 3

-- Method #1 
update emp set MANAGERNAME= mgr.EMPNAME 
FROM SelfJoinTable emp , SelfJoinTable mgr where emp.MANAGERID = mgr.EMPID 

-- Method #2 
update emp 
set MANAGERNAME= mgr.EMPNAME 
FROM SelfJoinTable emp 
    LEFT OUTER JOIN SelfJoinTable mgr 
    ON emp.MANAGERID = mgr.EMPID 

-- Method #3 
update emp 
set MANAGERNAME= mgr.EMPNAME 
FROM SelfJoinTable emp 
    JOIN SelfJoinTable mgr 
    ON emp.MANAGERID = mgr.EMPID 

-- Method #4 
update emp 
set MANAGERNAME= mgr.EMPNAME 
FROM SelfJoinTable emp 
    inner JOIN SelfJoinTable mgr 
    ON emp.MANAGERID = mgr.EMPID