I have written down this query in postgres sql with column alias it is working fine: <pre class="prettyprint"><code>select email as e from users </code></pre> It displays me result under <code>e</code> column alias but when I fire <code>where</code> condition with <code>e</code> then it shows this error: <pre class="prettyprint"><code>select email as e from users where e = 'jaskaransingh@demo.com' </code></pre> <blockquote> ERROR: column "e" does not exist </blockquote> Why so? How we can use alias in where condition?

<code>where</code> is evaluated before <code>select</code>, so you can't use alias declared in <code>select</code> in <code>where</code> clause.

Refer to a column name alias in the WHERE clause [duplicate]

I have written down this query in postgres sql with column alias it is working fine:

select email as e from users

It displays me result under e column alias but when I fire where condition with e then it shows this error:

select email as e from users where e = '[email protected]'

ERROR: column "e" does not exist

Why so? How we can use alias in where condition?

where is evaluated before select, so you can't use alias declared in select in where clause.