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thousands or millions of detail records that are queried and summarized but are not typically updated. Executive information systems (EIS) and data warehouses are examples of these types of applications. Either way, the needs are quite a bit different than those for an OLTP system. If you have a busy OLTP system, you might want to consider such factors as how a given database performs record locking. Sybase, for instance, uses what is called page-level locking—all records on a database page are locked when an update is to occur. Oracle, on the other hand, performs row-level locking—only those rows that are to be updated get locked. The record locking has implications if several users are trying to update different records on the same page. With the Sybase product, the users have to wait until the first user has released the lock on that page. Microsoft SQL Server 6.0 performs page-level locking, whereas SQL Server 6.5 does pseudo row-level locking: The rows immediately before and after the row to be updated are also locked. SQL Server 7.0 performs true row-level locking. On the other hand, the nature of your data may be such that a page contains few rows, which makes the issue of row-level versus page-level locking less important. If you are planning a DSS, you should consider how well the database handles very large volumes of data. Most of the major vendors support some sort of variation on massively parallel processing (MPP), where a long-running query is executed in multiple threads to better handle the intensive querying and to speed up processing. Determining which database will best handle your needs for an OLTP or a DSS is not an easy undertaking. My recommendation is to talk to peers who have used the products in environments similar to your own. In addition, check out the computer press for its independent benchmarking results. Lastly, consider searching the Internet (but avoid the vendor’s own biased claims). Previous Table of Contents Next Products | Contact Us | About Us | Privacy | Ad Info | Home Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc. All rights reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy statement.
Brief Full Advanced Search Search Tips To access the contents, click the chapter and section titles. Visual Basic 6 Client/Server Programming Gold Book (Publisher: The Coriolis Group) Author(s): Michael MacDonald and Kurt Cagle ISBN: 1576102823 Publication Date: 10/01/98 Search this book: Previous Table of Contents Next Number Of Users And Volume Of Data Considering both the number of users and the volume of data actually goes hand-in-hand with the prior discussion of database usage patterns. If you have two users who need access to only a few thousand records, by all means, consider a product such as Microsoft Access. If, on the other hand, you have many thousands of simultaneous users chasing terabytes of data, you need to examine the beefier databases such as Oracle, Sybase, Informix, Microsoft SQL Server, and DB2. If your needs are greater than what Access can satisfy but are perhaps less than what a database such as Oracle warrants, you might want to consider Sybase SQL Anywhere. My experiences with this product are that it can satisfy the needs of up to 50 users in a moderately heavy OLTP environment. For low volumes of data, you may be able to push the number of users to 100. For moderately sized databases, it is a viable platform for a DSS but does not offer the tools that an Oracle or Sybase SQL Server offers for massively parallel processing. Database Administration My own subjective experience is that Oracle’s database engine is probably the most powerful in a high-transaction environment. However, this power comes at the expense of more complicated administration. To squeeze the best performance out of a complex database product such as Oracle, the database administrator (DBA) needs to monitor and refine a variety of operating parameters, such as defining the frequency of checkpoints, partitioning the data, and so on. (The particulars of database administration vary from database to database and are beyond the scope of this book.) How much administration is required also depends on the nature of the applications that the database supports in your own organization.
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Page 5 and 6: Index Products | Contact Us | About
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Brief Full Advanced Search Search T
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SELECT EMP_NO AS 'NUMBER', EMP_LNAM
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FROM EMPLOYEE The result is: MIN(EM
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GENEVIEVE WESLEY The LTRIM function
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(15, 2) returns 1 because 15 divide
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SELECT SUM(EMP_SALARY) FROM EMPLOYE
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300 66958.36 400 53983.02 You can n
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ORDER BY EMP_DEPT_NO The output of
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SELECT EMP_NO, EMP_FNAME, EMP_LNAME
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the ODBC API as a means of database
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DAO/Jet * 4 7 5 6 DAO/ODBCDirect Da
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Listing 4.1 opens three files (in A
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Dim sBuffer As String * 512 Get #iF
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ODBCDirect was added to DAO with ve
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later in this chapter. For new rela
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End Sub Figure 4.5 The Employee app
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Listing 4.3 Code from frmDSNList. P
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When placing a data-aware control o
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Str$(Adodc1.RecordSet.RecordCount)
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similar to general modules in that
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source to other objects, including
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If bCancel Then adStatus = adStatus
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Structured Query Language, which li
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Figure 5.1 DAO objects in the Jet w
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dbVersion11 new_db will be the Jet
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collection after database operation
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dbDecimal Decimal dbDouble Double d
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nested transactions in an ODBCDirec
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wrkEmp.BeginTrans ' Start of inner
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Set User = object.CreateUser (name,
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three properties: Name, Password, a
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Database Type Specifier Example Mic
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QueryDef object and thus omits the
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this, specify a URL instead of a fi
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topic. Connection also has a Cancel
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docTemp.Properties.Append prpTemp d
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property is useful when two users m
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ForeignName property is set to the
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• The Primary property is a Boole
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' Display how many unique values th
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current object should be replicated
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"EMP_LNAME, EMP_SALARY FROM EMPLOYE
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set automatically reflects the chan
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workspaces. In a Jet workspace, BOF
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each record in the RecordSet. The c
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occurrences. FindLast finds the las
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Products | Contact Us | About Us |
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chapter provides an example of usin
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End Sub Table 5.15 Constants for th
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loaded as it does in DAO, and RDO p
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doEngine object is created. Additio
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messages (ODBC SQL_SUCCESS_WITH_INF
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Previous Table of Contents Next Pro
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in an rdoEnvironment object, all rd
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If cSalary !emp_Salary Then ' If c
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password parameters are not supplie
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The rdoConnections Collection And r
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Command1(0).Enabled = True Command1
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Dim vErr As rdoError For Each vErr
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objects. If the query was successfu
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embrace where two processes lock ea
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Connect:="UID=Coriolis;PWD=Coriolis
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If MsgBox(sMsg, vbYesNo & vbQuestio
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pbStatus.Value = .PercentPosition D
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cannot be updated. If the columns r
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Dim vArray As Variant ' Get 100 row
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modified. You can set the Cancel ar
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The SourceColumn and SourceTable pr
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stored procedures from Visual Basic
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Figure 6.6 The RDO parameters demon
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Private Sub MSRDC1_Error(Number As
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With VB6 comes MDAC 2.0, which adde
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Remote Data Services (RDS) is a dev
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adGUID Globally unique identifier (
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(ByVal pError As ADODB.Error, _ adS
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that few records are affected and a
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adXactChaos (Default.) Cannot overw
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(adSchemaTables, Array(Empty, Empty
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Dim sTable As String sTable = lbTab
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Figure 7.6 Message from the data so
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A value of 0 specifies that there i
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• The Direction property is used
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To move through a set of records, y
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ByVal pRecordset As ADODB.Recordset
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adOpenStatic. If you will be perfor
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as an argument the number of record
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FileName argument is self-explanato
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OriginalValue property contains the
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ADO, RDO, and DAO are roughly analo
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it exploits enough different method
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"UID=Coriolis;PWD=Coriolis" Set aco
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You must modify the connection stri
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' Display the results With arsRepor
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Objects library to Microsoft Active
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lbTables(0).AddItem ars.Fields(1).V
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e automatically created (!). To use
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eing the data source of a Command o
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default caption. I did this for the
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4. Now, you will need to add naviga
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txtRaise(2) = deStoredProcedure.Com
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object’s name by prefixing it wit
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The DataReport object supports a nu
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Command object represents a band in
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ight-click on the Flexgrid control
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Select Case dir Case rsFirst rs.Mov
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ByVal pConnection As ADODB.Connecti
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If IsNull(rs(iRs).Fields(iCtr - iSt
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possible. In fact, the nature of VB
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To map the properties, select Proce
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object in component based developme
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If Len(first) = 0 Or Len(last) = 0
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Figure 10.2 Once you declare a refe
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Private Sub Graphics_PrintIt(Target
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The next example modifies the Print
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End Select End Sub I will show you
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sMsg = "The following errors were e
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Private WithEvents empCLSDemo As cl
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triggered. In that event, I invoke
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Why go to all this trouble? Figure
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object. In a sense, the class modul
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Optimizing Cross-Process Calls As n
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start it in a separate instance of
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this method remotely, and I was for
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.Height = (iIndex * 360) + 1850 .Sh
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All of the code in both the remote
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the data dictionary. I will then le
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number of solutions. Previous Table
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CTRY_NAME VARCHAR (35) NOT NULL, CO
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dd_desc VARCHAR (64), CONSTRAINT PK
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Public when the application opens:
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cannot take an Oracle stored proced
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efficient), I chose to use the sp_l
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' Command object for the stored pro
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End Function When ADO dynamically c
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RETURN ; END IF ; /* If country sta
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FROM data_dic WHERE dd_type = old_d
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Figure 11.3 The Data Dictionary Mai
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data type—its underlying data typ
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CommitTrans Else RollbackTrans End
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any money. At worst, it should at l
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update to Cindy failed but the upda
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UPDATE employee SET emp_salary = 50
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difficult to update. With XML, the
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Raining on and off throughout the
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library in your Visual Basic projec
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ReplaceNode Replaces one node with
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Public WithEvents DownloadTimer As
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Sunny and hot. Raining on a
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Of course, it would be useful to ge
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Recursion is a powerful programming
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Dim Index As Integer Dim tempNode A
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End Sub You could create a simple X
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Figure 12.4 A DTD makes it much eas
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The DTD is contained as part of th
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In addition to enumerated lists, th
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Skies will be clear and warm today,
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which relies heavily on line breaks
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&ALABAMA; &ALASKA; &ARIZONA; ... &W
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can also leverage the powers of DHT
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information, usually a structured s
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somewhat in sales. IIS introduced A
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client side scripting is fully visi
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happening than just the creation of
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Cookies A collection of cookies tha
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8. Select the WeatherSummary object
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for all these possible additional p
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• Query strings have a limit of 1
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eturns it as a formatted string. Fu
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The Daily Post As mentioned previou
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4. Double-click the weatherSubmitFo
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If Request.Form("Forecast")="" then
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shows the actual Web event connecti
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in the record are modified and then
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the list of all states, ordered by
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Response.Write "" Response.Write Re
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same format as a rainfall map. A We
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still using Internet Explorer 3.x a
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Figure 14.5 The standard Properties
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Figure 14.10). Notice that the docu
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The highlighted code in Listing 14.
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CtrlKey Boolean True if the Ctrl ke
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collections, many of which are cove
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ClearInterval(timerID as Long) Clea
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Prompt(msg as String, defaultStr as
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OuterText=textString OuterText=“T
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Mouse Data The STYLE=“positio
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as a or paragraph element, accumul
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Dim expn As String expn = TextData
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uffer = buffer + expn WriteLn = exp
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Dim rowOS as COStream 'Set the dest
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example, if you wish to retrieve th
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Dim cell As HTMLTableCell Dim row A
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While on the subject of the parentW
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Understanding Input Text boxes and
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High Temperature:° F Low Tempe
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For index = 0 To lbCtrl.Length - 1
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Exit For End If Next RS.Close conn.
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State = States.Value Set WeatherTab
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Scrollbars Built into containers Th
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A little searching reveals that, in
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Set opt = Document.createElement("O
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Figure 15.1 The Project Properties
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HSPACE=0 > 2. Create a new DHTML
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loop Img.loop=3 Indicates the numbe
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useMap Img.useMap=“#MyMap” Prov
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there are times (especially with We
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associating code as with ExecFuncti
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tools. The tag demonstrates both t
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style rules that you need, as shown
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posLeft, MyDiv.style.posLeft=20 Set
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This is some text This is anoth
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sheet’s rule. Listing 15.7 The Ge
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slt=document.parentWindow.confirm("
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Answer=window.showModalDialog(URL,a
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Visual Basic 6 includes two new use
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ibliography at the end of this chap
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The calendar object is de
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Comment.Value = Replace(RS("Comment
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goods at all stages of production,
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DEPT_LOC_ID CHAR (3) NOT NULL, DEPT
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ALTER TABLE LINE_ITEM ADD CONSTRAIN
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COMMIT, ROLLBACK, And LOCK ANSI SQL
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VAR returns the variance (the squar
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RDO is loaded instead. However, whe
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Level 2 Conformance Requirements
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objects, 374 proxy objects and, 18
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B Application Wizard, 125, 619 Appl
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C Bound controls, 202 Boyce-Code no
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doConnection object, 235 rdoResults
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Connection object, 278 parameters,
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Microsoft Jet and, 105 object cross
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QueryTimeOut property, 159 RecordsA
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Debug mode, 618 DECIMAL (38) data t
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E Documents collection, 138, 168-16
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F properties, 288 Source property,
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G FLOATING POINT data type, 46 Floa
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I Hello World application, 511-514,
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delegation, 122 reuse, 121-122 Inhe
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doResultset object, 245-246 RecordS
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N MIN function, 79, 80 Minimum ODBC
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O NodeValue property, 472 NoMatch p
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P OpenSchema method, 284, 324, 327-
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Q prop_type string, 148 prop_val st
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licensing fees, 35 Lotus Approach,
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doCreateEnvironment property (rdoEn
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doVersion property (rdoEngine objec
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ValidationText property, 196 Record
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S ResultChanged event (rdoResultset
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Snapshot-type record set, 189 SNF.
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T Strings, 45 XML attribute values
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U Connection object, 165 rdoConnect
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W RecordSet object, 196 TableDef ob
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X Type property, 151 UserName prope
show all

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