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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:
Implicit Rollbacks Before execute the INSERT, UPDATE, or DELETE statement, the Oracle marks an implicit savepoint . When the statement fails, the Oracle rolls back to the save
Closing a Cursor The CLOSE statements disable the cursor, and the result set becomes undefined. An illustration of the CLOSE statement as shown: CLOSE c1;
Recursion versus Iteration Dissimilar the iteration, recursion is not crucial to PL/SQL programming. Any problem which can be solved using recursion can be solving using the it
Use of Table Comparisons - SQL Table comparisons where it is noted that although table expressions cannot be compared, we have TABLE (t) to convert a table expression t into
Avoid the NOT NULL Constraint In the PL/SQL, using the NOT NULL constraint incur a performance cost. Consider the illustration as shown below: PROCEDURE calc_m IS m NUMB
Blocks: The fundamental program unit in the PL/SQL is the block. The PL/SQL block is defined by the keywords BEGIN, DECLARE, EXCEPTION, and END. These keywords partition the b
OUT Mode An OUT parameter returns values to the caller of a subprogram. Within the subprogram, an OUT parameter act like a variable. That means that you can use an OUT formal
UNNEST operator in SQL The inverse operator of GROUP is UNGROUP. SQL has an operator, UNNEST, that can be used for similar purposes, but its method of invocation is somewhat p
%TYPE: This attribute gives the datatype of a formerly declared collection, cursor variable, object, field, record, database column, or variable. Datatype: This is simply
Datatype Conversion At times it is necessary to convert a value from one datatype to another. For e.g. if you want to inspect a rowid, you should convert it to a character stri
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