![]() ![]() You can’t, for example, change the table definition after the initial DECLARE statement. There are a few anomalies to be aware of too. However, once the dynamic SQL is run, there would be no table variable You can, of course, create, and then use, the table variable inside the dynamic SQL because the table variable would be in scope. This is because you can’t refer an externally-defined table variable within dynamic SQL that you then execute via the EXEC statement or the sp_ExecuteSQL stored procedure because the dynamic SQL is executed outside the scope of the table variable. One difficulty is that table variables can only be referenced in their local scope, so you cannot process them using dynamic SQL as you might with a temporary table or table-valued parameter. If your application is conservative and your data volumes light you’ll never want anything else. The downside of table variables is that they are often disposed of before you can investigate their contents for debugging, or use them to try out different SQL expressions interactively. Transaction rollbacks do not affect them because table variables have limited scope and are not part of the persistent database, so they are handy for creating or storing data that ought to survive roll backs such as log entries. Table variables require less locking resources as they are ‘private’ to the process that created them. These are much easier to work with, and pretty secure, and they also trigger fewer recompiles in the routines where they’re used than if you were to use temporary tables. They behave like other variables in their scoping rules. However, they are good for many of the uses that the traditional temporary table was put to. ![]() Table variables are used within the scope of the routine or batch within which they are defined, and were originally created to make table-valued functions possible. Just occasionally, you may need to fine-tune them to get good performance from them in joins, but I’ll explain that in a moment, However, if you are doing more complex processing on temporary data or likely to use more than reasonably small amounts of data in them, then local temporary tables are likely to be a better choice. They also tend to cause fewer problems to a hard-working OLTP system. They’re easy, and SQL Server does the work for you. Temporary tables come in different flavours including, amongst others, local temporary tables (starting with #), global temporary tables (starting with #), persistent temporary tables (prefixed by TempDB.), and table variables.(starting with we get too deep into the technology, I’d advise that you should use table variables where possible. Once finished with their use, they are discarded automatically. They are also used to pass a table from a table-valued function, to pass table-based data between stored procedures or, more recently in the form of Table-valued parameters, to send whole read-only tables from applications to SQL Server routines, or pass read-only temporary tables as parameters. ![]() They are used most often to provide workspace for the intermediate results when processing data within a batch or procedure. Temporary tables in SQL Server are just that. Temporary Tables in SQL Server - Simple Talk ![]()
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