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the WHERE clause should be per each SELECT.<br />

<pre><code id="code-164223">SELECT ...
  FROM ...
 WHERE ...
 GROUP BY ...
UNION ALL
SELECT ...
  FROM ...
 WHERE ... 
 GROUP BY ...
</code></pre>
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the WHERE clause should be per each SELECT.


SELECT ...
  FROM ...
 WHERE ...
 GROUP BY ...
UNION ALL
SELECT ...
  FROM ...
 WHERE ... 
 GROUP BY ...


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This should be a simple question...<br />
<br />
I am using UNION to join multiple tables with the same columns. At the end of the my UNION I am aliasing the whole thing as a tableX. After that I have a WHERE statement and a GROUP statement. Efficiency is of great importance! I want to know if it makes a difference from an effeciency standpoint if I repeat the WHERE and GROUP clause with each table in the union, or if I just have it at the end after the alais.
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This should be a simple question...

I am using UNION to join multiple tables with the same columns. At the end of the my UNION I am aliasing the whole thing as a tableX. After that I have a WHERE statement and a GROUP statement. Efficiency is of great importance! I want to know if it makes a difference from an effeciency standpoint if I repeat the WHERE and GROUP clause with each table in the union, or if I just have it at the end after the alais.

Where to put the Where Clause

Microsoft SQL Server 2005 is a suite of relational database management system (RDBMS) products providing multi-user database access functionality.Component services include integration (SSIS), reporting (SSRS), analysis (SSAS), data quality, master data, T-SQL and performance tuning. It includes support for managing XML data and allows a database server to be exposed over web services using Tabular Data Stream (TDS) packets encapsulated within SOAP (protocol) requests.

Microsoft SQL Server 2005

SQL (Structured Query Language) is designed to be used in conjunction with relational database products as of a means of working with sets of data. SQL consists of data definition, data manipulation, and procedural elements. Its scope includes data insert, query, update and delete, schema creation and modification, and data access control.