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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:
Effects of NULL for union - SQL The treatment of NULL in invocations of EXCEPT is as for UNION. This is different from its treatment in those of NOT IN and quantified compari
UNION without CORRESPONDING - SQL The use of UNION without CORRESPONDING. Example is merely by omitting CORRESPONDING, but only because the operands have identical SELECT clau
PL SQL Code Review HEADER ELEMENTS File Name Clear, meaningful and descriptive about main objective of the file. Multiple words are joined using underscores which adh
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
Logical Operators The logical operators AND, NOT, and OR follow the tri-state logic shown in table below. The AND and OR are binary operators; NOT is a unary operator.
Fetching from a Cursor Variable The FETCH statement retrieve rows one at a time from the product set of a multi-row query. The syntax for the same is as shown: FETCH {curso
Functions The function is a subprogram that calculates a value. The Functions and procedures are structured similar, except that the functions have a RETURN clause. You can
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
Obtaining a natural join by specifying the common columns Synatax: SELECT * FROM IS_CALLED JOIN IS_ENROLLED_ON USING ( StudentId ) However, a named columns join doe
Dynamic Ranges The PL/SQL lets you determine the loop range dynamically at run time, as the example below shows: SELECT COUNT(empno) INTO emp_count FROM emp; FOR i IN 1..emp_cou
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