barcode generator in vb.net 2005 Querying Collection Data in Software

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Querying Collection Data
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Collection-valued columns complicate the process of querying the tables that contain them. In the SELECT item list, they generate multiple data values for each row of query results. In search conditions, they don t contain individual data items, but it s sometimes convenient to treat them as sets of data. The object-relational databases typically provide a limited set of
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24:
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SQL and Objects
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SQL extensions or extend existing SQL concepts to provide simple queries involving collection data. For more advanced queries, they require you to write stored procedure language programs with loop structures that process the collection data items one by one. For query purposes, Informix treats the collection types as if they were a set of data values, like the values that might be returned by a subquery. You can match individual items within a collection using the SQL IN search condition. Here is a query that finds any technicians who work on a project named bingo :
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SELECT EMPL_NUM, NAME FROM TECHNICIANS WHERE 'bingo' IN (PROJECTS);
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The name of the collection-valued column (in this case, the set-valued column PROJECTS) appears in parentheses. Informix treats the members of the collection as a set and applies the IN matching condition. In interactive SQL, you can put a collection-valued column in the select item list. Informix displays the collection of data as a SET, LIST, or MULTISET in the displayed output. To process collection-valued data in the select list of a programmatic request (that is, from a program using ESQL or a call-level API), you must use special API extensions and/or extensions to the Informix stored procedure language. Oracle provides additional capabilities for processing nested tables within SQL queries. Newer versions offer a special function named TABLE that flattens the nested table, producing, in effect, an unnested table with one row for each row of the nested table within each row of the main table. (In older versions of Oracle, a special keyword THE, now deprecated, provided the same result, but with substantially different syntax.) Here s a query that uses the TABLE function to show the schools from which one of the engineers has received degrees:
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SELECT T2.SCHOOL FROM ENGINEERS T1, TABLE(T1.DEGREES) T2 WHERE EMPL_NUM = 1234;
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The FROM clause first references the ENGINEERS table that contains the nested table DEGREES, giving it the alias name T1. The TABLE function then uses the alias T1 to qualify the name of the nested table DEGREES. You can use the real table name if you qualify it with the nested table, such as ENGINEERS.DEGREES. The function flattens the nested table, creating a row for each nested row within each row of the main table, much like you would see if DEGREES were a separate table and you joined it with the main table. With this syntax, the SELECT clause in this example is quite simple; it selects one column that originated in the nested table. The ability to flatten nested tables in this way and process them as if they were actually joined versions of two separate tables is actually quite powerful. It allows many queries to be expressed in high-level SQL that would otherwise require you to resort to stored procedures. However, the logic behind such queries and the task of actually constructing them correctly can be complicated, as even this simple example begins to show.
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PART VI
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Manipulating Collection Data
Extensions to standard SQL syntax are used to insert new rows into a table containing collection-valued columns. Informix provides a trio of constructors the SET constructor,
Part VI:
SQL Today and Tomorrow
MULTISET constructor, and LIST constructor for this purpose. They transform a list of data items into the corresponding collections to be inserted. Here is a pair of Informix INSERT statements that illustrates their use with the tables in Figure 24-6:
INSERT INTO TECHNICIANS VALUES (1279, ROW('Sam', 'R', 'Jones'), ROW('164 Elm St.', 'Highland', 'IL', ROW(12345, 6789)), SET{'atlas', 'checkmate', 'bingo'}); INSERT INTO ENGINEERS VALUES (1281, ROW('Jeff', 'R', 'Ames'), ROW('1648 Green St.', 'Elgin', 'IL', ROW(12345, 6789)), MULTISET{ROW('BS', 'Michigan'), ROW('BS', 'Michigan'), ROW('PhD','Stanford')});
The first statement inserts a single row into the TECHNICIANS table with a three-item set in the PROJECTS column. The second inserts a single row into the ENGINEERS table with a three-item multiset in the DEGREES column. Because the members of this particular multiset are themselves row types, the row constructor must be used for each item. Oracle uses a different approach to constructing the collection-valued data items for insertion into the table. Recall from the discussion of Oracle abstract data types that each Oracle abstract data type automatically has an associated constructor method that is used to build a data item of the abstract type out of individual data items. This concept is extended to varying arrays and nested tables. A constructor method is automatically supplied for each varying array or nested table, and it is used in the INSERT statements:
INSERT INTO REPS (EMPL_NUM, NAME, ADDRESS, QTR_TGT) VALUES (109, NAME_TYPE('Mary', 'X', 'Jones'), ADDR_TYPE('164 Elm St.', 'Highland', 'IL', POST_TYPE(12345, 6789)), TGT_ARRAY(5000, 5000, 8000, 12000)); INSERT INTO ENGINEERS (EMPL_NUM, NAME, ADDRESS, DEGREES) VALUES (1281, NAME_TYPE('Jeff', 'R', 'Ames'), ADDR_TYPE('1648 Green St.', 'Elgin','IL', POST_TYPE(12345, 6789)), DEGR_TABLE(DEGR_TYPE('BS', 'Michigan'), DEGR_TYPE('BS', 'Michigan'), DEGR_TYPE('PhD', 'Stanford')));
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