Updating postgresql lesson of desire dating game
If the item already exists, instead update the stock count of the existing item.To do this without failing the entire transaction, use savepoints.In other words, a target row shouldn't join to more than one row from the other table(s).If it does, then only one of the join rows will be used to update the target row, but which one will be used is not readily predictable.If you see anything in the documentation that is not correct, does not match your experience with the particular feature or requires further clarification, please use this form to report a documentation issue. If you update values in multiple columns, you use a comma (,) to separate each pair of column and value.Therefore it is not necessarily possible to directly specify which row to update.
The new column value can be any scalar expression, not just a constant.
The columns that are not on the list retain their original values.
There are two ways to modify a table using information contained in other tables in the database: using sub-selects, or specifying additional tables in the you should ensure that the join produces at most one output row for each row to be modified.
For example, if you want to raise the price of all products by 10% you could use: condition does not have to be an equality test.
Many other operators are available (see Chapter 9).
Because of this indeterminacy, referencing other tables only within sub-selects is safer, though often harder to read and slower than using a join.