The SQL code equivalent is (from here): and check if it’s for a duplicate entry (my identifier field has a primary key — unique — constraint).
Every time you launch a Java applet, a Java Web Start application or the Java Control Panel, the system first launches your program and then, in the background (so that performance of your Java application is not impacted), it determines if it has checked in the last 7 days for a Java update.
If you choose Skip This Version, but later decide to check for an update, you can launch the Java Control Panel by clicking the Java icon in System Preferences. If you choose Remind Me Later, you will be reminded of the update the next time you run Java.
When the subquery fails to find a matching row in tbl B, the subquery returns NULL.
But since the UPDATE has no WHERE clause, it will update all rows, even those where the subquery returns NULL.
Consequently, to prevent this, you might do this: One potential issue may arise when the subquery actually finds more than one matching row in tbl B.