Using An Alias

CommentsProcedural SQL (PSQL) Statements

Using an alias

If you assign an alias to a table or a view, the alias must be used when specifying columns and also in any column references included in other clauses.

Example

Correct usage:

update Fruit set soort = 'pisang' where ...

update Fruit set Fruit.soort = 'pisang' where ...

update Fruit F set soort = 'pisang' where ...

update Fruit F set F.soort = 'pisang' where ...

Not possible:

update Fruit F set Fruit.soort = 'pisang' where ...

The `SET` Clause

In the SET clause, the assignment expressions, containing the columns with the values to be set, are separated by commas.In an assignment expression, column names are on the left and the values or expressions to assign are on the right.A column may be assigned only once in the SET clause.

A column name can be used in expressions on the right.The old value of the column will always be used in these right-side values, even if the column was already assigned a new value earlier in the SET clause.

Using the expression DEFAULT will set the column to its default value (either NULL or the value specified on the DEFAULT clause of the column definition).For an identity column, specifying DEFAULT will generate a new identity value.It is possible to “update” calculated columns in the SET clause if and only if the assigned value is DEFAULT.

Note	It is not possible to assign `DEFAULT` as a parameter value.

Here is an example

Data in the TSET table:

A B
---
1 0
2 0

The statement:

UPDATE tset SET a = 5, b = a;

will change the values to:

A B
---
5 1
5 2

Notice that the old values (1 and 2) are used to update the b column even after the column was assigned a new value (5).

Using An Alias

Using an alias

Example

The SET Clause

The `SET` Clause