Selceting and updating records oracle


This is why this approach is called pessimistic locking.

When the subquery fails to find a matching row in tbl B, the subquery returns NULL.A data manipulation language (DML) is a family of syntax elements similar to a computer programming language used for selecting, inserting, deleting and updating data in a database.Performing read-only queries of data is sometimes also considered a component of DML.Example: Table A: 1,2,3,1 Table B: 2,1,3,3 Result Table C: 2,1,1,3 As is common with SQL, there are several ways to skin this cat.

Perhaps the most simple would be to use an EXISTS clause with a correlated sub-query, like this: Using an inner join would work too, if we were dealing with distinct rows from table B.There have been a number of standards established for SQL by ANSI, but vendors still provide their own extensions to the standard while not implementing the entire standard.


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