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Re: Uniform UPDATE queries

From: Rob Sargent <robjsargent(at)gmail(dot)com>
To: pgsql-sql(at)postgresql(dot)org
Subject: Re: Uniform UPDATE queries
Date: 2012-04-18 15:10:43
Message-ID: 4F8ED973.8050305@gmail.com (view raw or flat)
Thread:
Lists: pgsql-sql
On 04/18/2012 04:11 AM, Dennis wrote:
> When a query is written to update a table, the usual process is to list
> all the columns that need updating. This could imply the creation of
> many possible queries for many columns. In an effort to keep the UPDATE
> queries more uniform, less number of unique queries, a keyword similar
> to DEFAULT, let's say CURRENT, is required to indicate that the current
> value must not change.
>
> Examples:
>
> update mytable set ( d ) = ("newvalue")
>
> This is the usual way to change values in column "d" and requires
> writing a new query for updating every column.
>
> update mytable set ( a, b, c, d ) = ( a, b, c, "newvalue" )
>
> This sort of works to change only column "d", but requires explicit
> naming of the columns on the value side.
>
> My suggestion is to introduce the CURRENT keyword:
>
> update mytable set ( a, b, c, d ) = ( CURRENT, CURRENT, CURRENT,
> "newvalue" )
>
> This could then lead to the uniform prepared JDBC statement:
>
> update mytable set ( a, b, c, d ) = ( ?, ?, ?, ? ) where id = ( ? );
>
> And then the JDBC driver could be improved to accept stmt.setString( 4,
> "newvalue" ) and automagically substitute the first three parameters
> with CURRENT when the query is executed. Note the added WHERE clause?
> The parameter for id is always on the same index. This makes the
> bookkeeping a lot easier and should reduce the need for generating
> UPDATE queries or even client JDBC code.
>
> -- Dennis Verbeek
>


Isn't this sort of shenanigans best left "one level up"?  The client/app 
code construct the requisite update statement since it knows which 
actual columns need updating (i.e. have dirty values).  This is actually 
quite straight forward when using O/R mapping tools such as hibernate or 
toplink (or whatever oracle calls it now).

rjs


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