java JPQL：在更新中将列设置为空
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/13039143/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
JPQL: set a column to null in an update
提问by AndrewBourgeois
The following JPQL:
以下JPQL：
UPDATE SignIn signIn SET signIn.cookieUUID = null WHERE signIn.user.id = :userID
Gives me the following error because of the "= null":
由于“= null”，给我以下错误：
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IS NULL WHERE `B0`.`ID` = 9' at line 1
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
But it works when I set the field to an empty string (= '').
但是当我将该字段设置为空字符串 (= '') 时它会起作用。
So how do you set a column to null using JQPL?
那么如何使用 JQPL 将列设置为空呢？
采纳答案by Yogendra Singh
I think its NULL(in caps) ::Reference JPQLand Eclipselink
我认为它NULL（大写）::Reference JPQL和Eclipselink
UPDATE SignIn signIn SET signIn.cookieUUID = NULL WHERE signIn.user.id = :userID
Or use param query as :
或使用参数查询为：
String sQuery = "UPDATE SignIn signIn SET signIn.cookieUUID = :cookieUUID "+
"WHERE signIn.user.id = :userID";
Query query= entityManager.createQuery(sQuery );
query.setParameter("cookieUUID", null);
query.setParameter("userID", userID);
query.executeUpdate();
