barcode generator vb.net download The Multirow INSERT Statement in Software

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The Multirow INSERT Statement
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The second form of the INSERT statement, shown in Figure 10-3, adds multiple rows of data to its target table. In this form of the INSERT statement, the data values for the new rows are not explicitly specified within the statement text. Instead, the source of new rows is a database query, specified in the statement.
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INSERT INTO table-name ( column-name , )
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Multirow INSERT statement syntax diagram
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Adding rows whose values come from within the database itself may seem strange at first, but it s very useful in some special situations. For example, suppose you want to copy the order number, date, and amount of all orders placed before January 1, 2008, from the ORDERS table into another table, called OLDORDERS. The multirow INSERT statement provides a concise, efficient way to copy the data: Copy old orders into the OLDORDERS table.
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INSERT INTO SELECT FROM WHERE OLDORDERS (ORDER_NUM, ORDER_DATE, AMOUNT) ORDER_NUM, ORDER_DATE, AMOUNT ORDERS ORDER_DATE < '2008-01-01';
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9 rows inserted.
This INSERT statement looks complicated, but it s really very simple. The statement identifies the table to receive the new rows (OLDORDERS) and the columns to receive the data, just like the single-row INSERT statement. The remainder of the statement is a query that retrieves data from the ORDERS table. Figure 10-4 graphically illustrates the operation of this INSERT statement. Conceptually, SQL first performs the query against the ORDERS table and then inserts the query results, row by row, into the OLDORDERS table. Here s another situation where you could use the multirow INSERT statement. Suppose you want to analyze customer buying patterns by looking at which customers and salespeople are responsible for big orders those over $15,000. The queries that you will be running will combine data from the CUSTOMERS, SALESREPS, and ORDERS tables. These three-table queries will execute fairly quickly on the small sample database, but in a real corporate database with many millions of rows, they would take a long time. Rather than running many long, three-table queries, you could create a new table named BIGORDERS to contain the required data, defined as follows:
Column AMOUNT COMPANY NAME PERF MFR PRODUCT QTY Information Order amount (from ORDERS) Customer name (from CUSTOMERS) Salesperson name (from SALESREPS) Amount over/under quota (calculated from SALESREPS) Manufacturer ID (from ORDERS) Product ID (from ORDERS) Quantity ordered (from ORDERS)
10:
Database Updates
ORDERS Table ORDER_NUM ORDER_DATE CUST 112961 113012 112989 113051 . . . 113049 112987 113057 113042 2007-12-17 2008-01-11 2008-01-03 2008-02-10 . . . 2008-02-10 2007-12-31 2008-02-18 2008-02-02 2117 2111 2101 2118 . . . 2118 2103 2111 2113 REP MFR PRODUCT 106 105 106 108 . . . 108 105 103 101 REI ACI FEA QSA . . . QSA ACI ACI REI 2A44L 41003 114X Xk47 . . . Xk47 4100Y 4100X 2A44R QTY AMOUNT
7 $31,500.00 35 $3,745.00 6 $1,458.00 2 $1,420.00 . . . . . . 2 $776.00 11 $27,500.00 24 $600.00 5 $22,500.00
SELECT ORDER_NUM, ORDER_DATE, AMOUNT FROM ORDERS WHERE ORDER_DATE < 2008-01-01 ;
OLDORDERS Table ORDER_NUM ORDER_DATE AMOUNT
Query Results ORDER_NUM ORDER_DATE 112961 112963 112968 112975 112979 112983 112987 112992 112993 AMOUNT
2007-12-17 $31,500.00 2007-12-17 $3,276.00 2007-10-12 $3,978.00 2007-10-12 $2,100.00 2007-10-12 $15,000.00 $702.00 2007-12-27 2007-12-31 $27,500.00 $760.00 2007-11-04 2007-01-04 $1,896.00
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FIGURE 10-4
Inserting multiple rows
Once you have created the BIGORDERS table, this multirow INSERT statement can be used to populate it: Load data into the BIGORDERS table for analysis.
INSERT INTO SELECT FROM WHERE AND AND BIGORDERS (AMOUNT, COMPANY, NAME, PERF, PRODUCT, MFR, QTY) AMOUNT, COMPANY, NAME, (SALES - QUOTA), PRODUCT, MFR, QTY ORDERS, CUSTOMERS, SALESREPS CUST = CUST_NUM REP = EMPL_NUM AMOUNT > 15000.00;
6 rows inserted.
In a large database, this INSERT statement may take a while to execute because it involves a three-table query. When the statement is complete, the data in the BIGORDERS table will duplicate information in other tables. In addition, the BIGORDERS table won t be automatically kept up to date when new orders are added to the database, so its data may quickly become outdated. Each of these factors seems like a disadvantage. However, the subsequent data analysis queries against the BIGORDERS table can be expressed very simply they become single-table queries. Furthermore, each of those queries will run much faster than if it were a three-table join. Consequently, this is probably a good strategy for performing the analysis, especially if the three original tables are large. In this situation, it s likely that the BIGORDERS table will be used as a temporary table for doing the analysis. It will be created and populated with data, representing a snapshot of the order status in time, the analysis programs will be run, and then the table will be emptied or dropped.
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