Portability InterBase doesn't support CASE The gain shown is for only seven DBMSs in Java

Create Data Matrix 2d barcode in Java Portability InterBase doesn't support CASE The gain shown is for only seven DBMSs
Portability InterBase doesn't support CASE The gain shown is for only seven DBMSs
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The batch-oriented method is reasonable if you are updating 100% of the rows in the table Generally you should be leery of statements that select everything and then decide what to do based on the selection such code might just be a transplant from a legacy system In this example, though, there is an advantage because the WHERE clauses are dispensed with, and because the rows are processed in ROWID order
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The Bottom Line: UPDATE
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Update multiple columns with the same UPDATE SET clause, rather than with multiple UPDATE statements UPDATE SET clause evaluation must be from left to right If any assignment is likely to fail, put it first in the SET clause It can be helpful to add a redundant WHERE clause to an UPDATE statement, in cases where it's possible that no rows need to be updated This won't work if any of the columns can contain NULL If you're updating all rows of a table, use batch processing for the UPDATE Check out ON UPDATE CASCADE (for a primary/foreign key relationship) if you find you're doing multiple UPDATE statements on related tables in sequence Consider whether columns belonging to multiple tables should belong to the same table if they're frequently being updated in sequence Put related and frequently done UPDATE statements into triggers and/or stored procedures
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DELETE
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The SQL Standard description of the typical DELETE format is:
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DELETE FROM <Table name> [ WHERE <search condition> ]
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The word FROM is optional for Microsoft and Sybase, but once again, there is no reason to leave it out and cause portability trouble Here's an example:
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DELETE FROM Table1 WHERE column1 = 55
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If all rows in the table are to be deleted, it's a better idea to execute DROP TABLE and then re-create the table, or to use a nonstandard SQL extension row-blaster For example Informix, Microsoft, and Sybase allow:
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TRUNCATE TABLE <Table name>
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And Ingres allows:
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MODIFY <Table name> TO TRUNCATED
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Such statements, however, do not allow for logging or for DELETE triggers But TRUNCATE has advantages it won't cause dropping of related constraints, indexes, or optimizer statistics Because you usually won't want these objects to be dropped in addition to the table, TRUNCATE involves less maintenance at rebuild time
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The Bottom Line: DELETE
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If all rows in the table are to be deleted, it's a better idea to execute DROP TABLE and then re-create the table or to use TRUNCATE TRUNCATE involves less maintenance
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Ugly Updates
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Microsoft and Sybase have trouble when a data-change statement causes row movement (what they call an out-of-place update) All DBMSs have trouble when a data-change statement causes temporary violation of UNIQUE constraints Ugly updates won't cause errors, but they are markedly slower than "regular" updates For example, the Big Eight take about 50% longer (on average) to do an out-ofplace update than a regular data-change statement The marks of an ugly update vary depending on DBMS, and even on DBMS version We have gathered together a list based on vendor recommendations Because the list is a composite, not all items on it will apply to any single DBMS Take it as a weak set of guidelines[2]
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These guidelines do not apply for InterBase, because InterBase stores a record of the difference (a "delta" record) instead of just replacing the original data
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A data change should affect only one row if a UNIQUE-indexed column is changed A wellknown problem with UNIQUE-indexed columns can be seen in this statement:
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UPDATE Table1 SET unique_column = unique_column + 1
If the current values in unique_column are {1, 2} and the DBMS updates only one row at a time, then after the first row is changed, the values in unique_column will be {2, 2} a violation of the UNIQUE constraint To avoid this situation, some DBMSs will do the UPDATE in two separate steps: First the DBMS will DELETE all the old values, then it will INSERT all the new values That's a solid solution but rather slow And it's unnecessary if the UPDATE statement contains a clause that makes it clear there's only one row to change, as in this example: