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SQL Server : Constraints and Rock Solid Inventory Systems (part 3) - Updating existing rows
Although we have now managed, with some difficulty, to modify a row in the middle of a history trail, we need to emphasize that only inserting rows at the end of history trail is fast and convenient. Correcting history is harder and may be significantly less performant.
SQL Server : Constraints and Rock Solid Inventory Systems (part 2) - Adding new rows to the end of the inventory trail
In SQL Server, a UNIQUE constraint disallows duplicate NULLs. However, according to the ANSI standard it should allow them. Therefore, the UNIQUE constraint in Listing 18 will work on SQL Server but will not port to a RDBMS that implements ANSI-compliant UNIQUE constraints.
SQL Server : Constraints and Rock Solid Inventory Systems (part 1)
To record any change in the inventory, we insert rows into the Inventory table. At the very beginning, when we do not have any rows in the InventoryLog table, we assume that we do not have any items in our inventory at all. An increase or decrease in inventory for a given item is reflected by adding new rows.
Oracle Database 11g : Learn the Difference Between Dedicated and Shared Server Architectures
An Oracle database server can be configured to run either a dedicated or shared server architecture. This decision determines how the listener processes requests and how server processes work for an Oracle instance.
Oracle Database 11g : Use Oracle Net Services
Oracle Net Services is the software component that allows enterprise connectivity across heterogeneous environments. Oracle Net is the part of Oracle Net Services that manages data communication between a remote application and the Oracle database; it runs on top of a network protocol like TCP/IP.
SQL Server 2008 : Issues When Triggers Using @@ROWCOUNT Are Fired by MERGE
The MERGE statement is a powerful new feature but, again, we need to be mindful of its use alongside existing code. In this example, I will demonstrate how a previously working trigger may start to misbehave when called from a MERGE statement.
SQL Server 2008 : When Upgrading Breaks Code - Understanding MERGE
The MERGE statement was introduced in SQL Server 2008 as a way to allow us to both insert new rows and update or delete existing ones, in a single command. The following simple example should demonstrate how it works, for those unfamiliar with it
SQL Server 2008 R2 : Optimistic Locking
With many applications, clients need to fetch the data to browse through it, make modifications to one or more rows, and then post the changes back to the database in SQL Server. These human-speed operations are slow in comparison to machine-speed operations, and the time lag between the fetch and post might be significant.
SQL Server 2008 R2 : Table Hints for Locking
You can set an isolation level for your connection by using the SET TRANSACTION ISOLATION LEVEL command. This command sets a global isolation level for an entire session, which is useful if you want to provide a consistent isolation level for an application.
MySQL for Python : Simple Insertion - Helpful ways to nuance an INSERT statement
Like SELECT has other helpful quantifiers to weed through the data being returned, INSERT has ways of nuancing the origin of the data to be inserted as well as the timing and conditions of the insertion.
MySQL for Python : Simple Insertion - Forming a MySQL insertion statement
Inserting data into MySQL through Python relies on understanding data insertion in MySQL itself. You will recall that the requirements of a computing language necessitate the use of as few words as possible to do anything.
SQL Server 2008 R2 : Locking Contention and Deadlocks (part 2) - Deadlocks
A deadlock occurs when two processes are each waiting for a locked resource that the other process currently holds. Neither process can move forward until it receives the requested lock on the resource, and neither process can release the lock it is currently holding until it can receive the requested lock.
SQL Server 2008 R2 : Locking Contention and Deadlocks (part 1) - Identifying Locking Contention
When a client application appears to freeze after submitting a query, this is often due to locking contention. To identify locking contention between processes, you can use the SSMS Activity Monitor; use the sp_who2 stored procedure; or query the sys.dm_tran_locks system catalog view.
SQL Server 2008 R2 : Locking and Performance - SQL Server Lock Granularity (part 3) - Index Locking, Lock Escalation
As with locks on data pages, SQL Server manages locks on index pages internally. There is the opportunity for greater locking contention in index pages than in data pages. Contention at the root page of the index is the highest because the root is the starting point for all searches via the index.
SQL Server 2008 R2 : Locking and Performance - SQL Server Lock Granularity (part 2) - Using Application Locks
The SQL Server Lock Manager knows nothing about the object or the structure of the object it is locking. The Lock Manager simply checks whether two processes are trying to obtain incompatible locks on the same resource. If so, blocking occurs.
SQL Server 2008 R2 : Locking and Performance - SQL Server Lock Granularity (part 1) - Serialization and Key-Range Locking
SQL Server provides serialization (Isolation Level 3) through the SET TRANSACTION ISOLATION SERIALIZABLE command. One of the isolations provided by this isolation level is the prevention against phantom reads.
SQL Server 2008 R2 : Locking and Performance - SQL Server Lock Types
Locking is handled automatically in SQL Server. The Lock Manager chooses the type of lock, based on the type of transaction (such as SELECT, INSERT, UPDATE, or DELETE).
Oracle Coherence 3.5 : Implementing Domain Objects - Domain model building blocks (part 3) - Factories, Repositories
The factories are useful when we need to create new instances of domain objects, but in many cases we simply need to retrieve the existing instances. In order to accomplish that, we can use a repository.
Oracle Coherence 3.5 : Implementing Domain Objects - Domain model building blocks (part 2)
Unlike entities, value objects are not uniquely identifiable within a system. They simply represent values from the domain, and are typically immutable (and if they are not, they probably should be).
Oracle Coherence 3.5 : Implementing Domain Objects - Domain model building blocks (part 1)
An entity is an object that has an identity. The identity can be either a natural attribute of an object or it can be a surrogate attribute that is generated by the system when the entity is first created. Regardless of the type of identity, what is important is that once an identity is assigned to an entity, it remains the same throughout its lifetime.
SQL Server 2008 R2 : Locking and Performance - Monitoring Lock Activity in SQL Server
The sys.dm_tran_locks dynamic management view returns information about all the locks currently granted or waiting to be granted in SQL Server. (The information is populated from the internal lock management structures in SQL Server 2008.)
SQL Server 2008 R2 : Locking and Performance - Transaction Isolation Levels in SQL Server
Isolation levels determine the extent to which data being accessed or modified in one transaction is protected from changes to the data by other transactions. In theory, each transaction should be fully isolated from other transactions.
SQL Server 2008 R2 : Query Analysis - Query Analysis with SQL Server Profiler
SQL Server Profiler serves as another powerful tool available for query analysis. When you must monitor a broad range of queries and database activity and analyze the performance, it is difficult to analyze all those queries manually.
SQL Server 2008 R2 : Query Analysis - Query Statistics
In addition to the new dynamic management objects, SQL Server 2008 still provides the SET STATISTICS IO and SET STATISTICS TIME options, which display the actual logical and physical page reads incurred by a query and the CPU and elapsed time, respectively.
SQL Server 2008 R2 : Query Analysis - Using sys.dm_exec_query_plan
Dynamic management views (DMVs) can return server state information that can be used to monitor and diagnose database engine issues and help tune performance. The sys.dm_exec_query_plan DMV returns the showplan information for a T-SQL batch whose query execution plan resides in the plan cache.
SQL Server 2008 R2 : Query Analysis - SSMS Client Statistics, Using the SET SHOWPLAN Options
Unlike the graphical execution plans, SSMS does not provide a way to save the client statistics. Fortunately, the statistics are displayed using a standard grid control. You can right-click the client statistics and choose Select All.
SQL Server 2008 R2 : Query Analysis in SSMS (part 2) - Logical and Physical Operator Icons
If you want to better understand the graphical execution plans displayed in SSMS, it helps to be able to recognize what each of the displayed icons represents. Recognizing them is especially valuable when you need to quickly locate operations that appear out of place for the type of query being executed.
SQL Server 2008 R2 : Query Analysis in SSMS (part 1) - Execution Plan ToolTips
When a graphical execution plan is presented in the Query Analyzer, you can get more information about each node in the execution plan by moving the mouse cursor over one of the icons.
SQL Server 2008 R2 : Implementing Data Integrity (part 5) - Using Constraints - Managing Constraints
Managing constraints consists of gathering information about constraints, disabling and re-enabling constraints, and dropping constraints. These actions are discussed in the following sections.
SQL Server 2008 R2 : Implementing Data Integrity (part 4) - Using Constraints - The CHECK Constraint, Creating Constraints
You can define constraints on a single column or on multiple columns. Single-column constraints are referred to as column-level constraints. You can define this type of constraint when you create the column on the table.
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