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UNION and OR - SQL
SQL supports UNION explicitly but differently from the way it supports JOIN explicitly. As we have seen, JOIN is used exclusively within the FROM clause, such that IS_CALLED NATURAL JOIN IS_ENROLLED_ON, for example, can be an element of that clause but cannot stand alone as a table expression. Instead, UNION always connects table expressions that can stand alone, these being:
Collection Methods: The collection method is a built-in function or procedure which operates on the collections and is called using the dot notation. The methods like the C
Inner Join We have learned how to retrieve data from one table by using SELECT statement. But, as we have learned, normalized relational databases mean the data is spread betw
Parameter and Keyword Description: table_reference: This keyword identifies the table or view that should be accessible when you execute the UPDATE statement, and for wh
Example of UNWRAP Operator - SQL Example here shows how unwrapping can be done in longhand in SQL. Example: Unwrapping in SQL Letting CONTACT_INFO_WRAPPED denote the res
Avoiding Collection Exceptions In many cases, if you reference a nonexistent collection element, then PL/SQL raises a predefined exception. Consider the illustration shown b
set serveroutput on declare a number(5); b number(5); c number(5); begin a:=&a; b:=&b; c:=a/b; dbms_output.put_line(c); exception when zero_divide then d
When Are Constraints Checked Under the model constraints are conceptually checked at all statement boundaries (and only at statement boundaries). By default the same is true
Cursor FOR Loops In most cases that need an explicit cursor, you can simplify the coding by using a cursor FOR loop rather of the OPEN, FETCH, and CLOSE statements. A cursor FO
Extension and AND in SQL The theory book gives the following simple example of relational extension in Tutorial D: EXTEND IS_CALLED ADD ( FirstLetter ( Name ) AS Initial )
What are 3 good practices of modeling and/or implementing data warehouses?
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