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POHow to avoid NULL when using Value-Name Mapping in SQL
 

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  1. POHow to avoid NULL when using Value-Name Mapping in SQL
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    <p>I have a table like the following which is basically used to "give a name" to a value in a table (this table contains values for a bunch of other tables as well, not just for MYTABLE; I've omitted a few irrelevant fields from NAMEVALUEMAP):</p> <pre><code>NAMEVALUEMAP Table --------------------- VALUE_ | NAME_ --------------------- 0 | ZERO 1 | ONE </code></pre> <p>I didn't want to use JOINs so I thought of using Sub-Queries.<br><br> Problem is when a value does not exist in the NAMEVALUEMAP table then NULL is shown.<br> Instead of NULL I want to show the actual value from MYTABLE (MYTABLE has ID field as identity column and contains a few rows):</p> <pre><code>-- //Fine, prints word 'ZERO' when MYTABLE.ABC is 0 SELECT (SELECT NAME_ FROM NAMEVALUEMAP WHERE VALUE_ = (SELECT ABC FROM MYTABLE inner_ WHERE inner_.ID = outer_.ID)) FROM MYTABLE outer_ -- //Not Fine, prints NULL (because "999" is not in NAMEVALUEMAP). In this case, MYTABLE.ABC is 999 -- //Want it to print 999 if the value is not in NAMEVALUEMAP SELECT (SELECT NAME_ FROM NAMEVALUEMAP WHERE VALUE_ = (SELECT ABC FROM MYTABLE inner_ WHERE inner_.ID = outer_.ID)) FROM MYTABLE outer_ -- //Tried COALESCE, but the error is "Invalid column name 'VALUE_'" SELECT COALESCE((SELECT NAME_ FROM NAMEVALUEMAP WHERE VALUE_ = (SELECT ABC FROM MYTABLE inner_ WHERE inner_.ID = outer_.ID)), ABC) FROM MYTABLE outer_ </code></pre> <p><strong>Also</strong>, is there <strong>a better way</strong> to do this sort of value-to-name mapping?</p>
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    1. COWhy don't you want to use joins?
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    2. COSeems like I'm wrong about JOINs being slower than sub-queries, at least in this case? Please see my reply to comments below as to what my reasoning is..
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