SQLFreeStmt SQLDisconnect SQLFreeConnect SQLFreeEnv in Java

Printer Data Matrix 2d barcode in Java SQLFreeStmt SQLDisconnect SQLFreeConnect SQLFreeEnv
SQLFreeStmt SQLDisconnect SQLFreeConnect SQLFreeEnv
Generating ECC200 In Java
Using Barcode encoder for Java Control to generate, create DataMatrix image in Java applications.
/* /* /* /*
Bar Code Generator In Java
Using Barcode creator for Java Control to generate, create bar code image in Java applications.
reverse reverse reverse reverse
Bar Code Reader In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
SQLAllocStmt */ SQLDriverConnect */ SQLAllocConnect */ SQLAllocEnv */
Data Matrix Creation In Visual C#.NET
Using Barcode drawer for Visual Studio .NET Control to generate, create DataMatrix image in VS .NET applications.
Many developers have performed this same exercise with the intent of copying Microsoft's basic methods The MS Query imitations all go through the same phases: a buildup with resource allocations, a series of SQLGetInfo and catalog-function calls, a point where an actual SQL statement goes down the line, some result processing, and teardown
Data Matrix ECC200 Generator In .NET Framework
Using Barcode drawer for ASP.NET Control to generate, create Data Matrix image in ASP.NET applications.
SQLPrepare
Drawing Data Matrix 2d Barcode In .NET
Using Barcode drawer for VS .NET Control to generate, create Data Matrix ECC200 image in .NET applications.
With ODBC, you can do an SQL statement in one function call:
Data Matrix ECC200 Generator In VB.NET
Using Barcode printer for Visual Studio .NET Control to generate, create Data Matrix 2d barcode image in VS .NET applications.
SQLExecDirect("<SQL statement>")
UPC-A Supplement 2 Creation In Java
Using Barcode generator for Java Control to generate, create UPCA image in Java applications.
or you can split it into two function calls:
UPC - 13 Printer In Java
Using Barcode maker for Java Control to generate, create EAN-13 image in Java applications.
SQLPrepare("<SQL statement>") SQLExecute()
Making Bar Code In Java
Using Barcode creator for Java Control to generate, create barcode image in Java applications.
Which is more efficient We measured the relative performance of both methods and found that SQLPrepare takes a significant fraction (averaging about 30%) of the total time If a statement is complex or if the number of rows affected is small, then it helps performance to take the preparation out of the loop, like this:
Create Barcode In Java
Using Barcode drawer for Java Control to generate, create barcode image in Java applications.
SQLPrepare("<SQL statement>") loop { SQLExecute() }
Data Matrix ECC200 Printer In Java
Using Barcode encoder for Java Control to generate, create Data Matrix ECC200 image in Java applications.
Taking an invariant assignment out of a loop is called hoisting We won't waste time showing it's a good idea because that's obvious What's important is to know when hoisting is not worthwhile If your DBMS caches SQL statements and reuses the plans, then hoisting is automatic so it's not worthwhile to do it yourself For example, you would see no gain if you use Oracle Hoisting may not be helpful if your intent is to generalize an SQL statement to take advantage of SQLPrepare For example, suppose you have these three queries:
Painting USS 93 In Java
Using Barcode generation for Java Control to generate, create ANSI/AIM Code 93 image in Java applications.
SELECT * FROM Table1 WHERE column1 = 'A' SELECT * FROM Table1 WHERE column1 = 'B' SELECT * FROM Table1 WHERE column1 = 'C'
Barcode Maker In .NET
Using Barcode creator for ASP.NET Control to generate, create bar code image in ASP.NET applications.
To execute the queries, you think that this looks like a clever idea:
EAN / UCC - 13 Generation In Visual Studio .NET
Using Barcode drawer for VS .NET Control to generate, create UCC-128 image in Visual Studio .NET applications.
SQLPrepare( "SELECT * FROM Table1 WHERE column1 = ") SQLBindParameter() /* to associate the with variable x */ x = 'A' SQLExecute()
Creating EAN 13 In VS .NET
Using Barcode drawer for ASP.NET Control to generate, create EAN-13 Supplement 5 image in ASP.NET applications.
x = 'B' SQLExecute() x = 'C' SQLExecute()
Bar Code Printer In VS .NET
Using Barcode encoder for Visual Studio .NET Control to generate, create barcode image in VS .NET applications.
For the general case, changing a literal to a parameter is good because the DBMS then has no need to reparse the statement multiple times and also because there will be fewer different statements to process Great but not always! The danger with this idea is that, although the three SQL statements look similar, the execution plans could be very different if the value A occurs far more frequently than B in the index If the optimizer knows what the literal is, it also knows whether it's common or uncommon and can modify the execution plan accordingly If you don't give the optimizer that information, then it has to use a generalized plan that might not be optimal at all Statements are not re-prepared when statistics change Thus, if the loop contains an implied transaction end, the preparation may become invalid making hoisting definitely not worthwhile For example, suppose you're updating:
Barcode Maker In C#
Using Barcode maker for .NET Control to generate, create bar code image in .NET applications.
SQLPrepare("<UPDATE statement>") loop { SQLExecute() }
Creating Bar Code In VS .NET
Using Barcode drawer for .NET Control to generate, create bar code image in Visual Studio .NET applications.
This sequence is doomed if the DBMS is in auto-commit mode, and if the DBMS invalidates PREPARE statements whenever it commits Admittedly though, you can get around that difficulty by calling SQLGetInfo(SQL_CURSOR_COMMIT_BEHAVIOR) and SQLGetConnectAttr(SQL_ATTR_AUTOCOMMIT) Here's a final reason to be cautious of hoisting In early versions of Microsoft, SQLPrepare causes the creation of a temporary table Make no mistake, the Boy Scout motto is correct It's just that "Be prepared" doesn't always mean "Call SQLPrepare" If you're afraid of it, then at least try this: Limit what users can enter (notice that most Internet dialog boxes give only a few options), and depend on the DBMS to reuse plans for queries that are exactly the same
Code 3/9 Encoder In C#.NET
Using Barcode generation for .NET Control to generate, create Code 39 image in VS .NET applications.
The Bottom Line: SQLPrepare
If a statement is complex or if the number of rows affected is small, take SQLPrepare out of the loop Do generalize an SQL statement to try and take advantage of SQLPrepare unless the query plan depends on a skewed set of data values If you must SQLPrepare, limit what users can enter, and depend on the DBMS to reuse plans for queries that are exactly the same