I'm reading a book about SQL. In that book there's the term Ad Hoc Query, which I don't understand.
What exactly is an ad hoc query?
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Ad hoc query is type of computer definition. Which means this query is specially design to obtain any information when it is only needed. Predefined. refer this https://www.youtube.com/watch?v=0c8JEKmVXhU
In Sql Server "Ad Hoc Query" is also used for Ad Hoc Distributed Queries. These are ad hoc queries on an other server via OpenRowset or OpenDatasource. Ad Hoc Distributed Queries are only allowed after configuring so. This is a Server configuration option.
Ad hoc queries are those that are not already defined that are not needed on a regular basis, so they're not included in the typical set of reports or queries
An Ad-Hoc Query is a query that cannot be determined prior to the moment the query is issued. It is created in order to get information when need arises and it consists of dynamically constructed SQL which is usually constructed by desktop-resident query tools. An ad hoc query does not reside in the computer or the database manager but is dynamically created depending on the needs of the data user.
In SQL, an ad hoc query is a loosely typed command/query whose value depends upon some variable. Each time the command is executed, the result is different, depending on the value of the variable. It cannot be predetermined and usually comes under dynamic programming SQL query. An ad hoc query is short lived and is created at runtime.
Also want to add that ad hoc query is vulnerable to SQL injection attacks. We should try to avoid using it and use parameterized SQLs instead (like PreparedStatement in Java).
An Ad-hoc query is one created to provide a specific recordset from any or multiple merged tables available on the DB server. These queries usually serve a single-use purpose, and may not be necessary to incorporate into any stored procedure to run again in the future.
Ad-hoc scenario: You receive a request for a specific subset of data with a unique set of variables. If there is no pre-written query that can provide the necessary results, you must write an Ad-hoc query to generate the recordset results.
Beyond a single use Ad-hoc query are stored procedures; i.e. queries which are stored within the DB interface tool. These stored procedures can then be executed in sequence within a module or macro to accomplish a predefined task either on demand, on a schedule, or triggered by another event.
Stored Procedure scenario: Every month you need to generate a report from the same set of tables and with the same variables (these variables may be specific predefined values, computed values such as “end of current month”, or a user’s input values). You would created the procedure as an ad-hoc query the first time. After testing the results to ensure accuracy, you may chose to deploy this query. You would then store the query or series of queries in a module or macro to run again as needed.
Ad-hoc Query -
An Ad-Hoc query is:
An Ad-Hoc Query is a query that cannot be determined prior to the moment the query is issued. It is created in order to get information when need arises and it consists of dynamically constructed SQL which is usually constructed by desktop-resident query tools.
Check: http://www.learn.geekinterview.com/data-warehouse/dw-basics/what-is-an-ad-hoc-query.html
Ad-hoc Statments are just T-SQL Statements that it has a Where Clause , and that Where clause can actualy have a literal like :
Select * from member where member_no=285;
or a variable :
declare @mno INT=285;
Select * from member where member_no=@mno
Source: Stackoverflow.com