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by croes 975 days ago
In an exists query select * is harmless, select 1 and select * result in the same execution plan at least in MS SQL.

In a query than returns result rows it could break the query as soon as you add columns with names that already exist in other tables you joined in the query.
1 comments
__jem 975 days ago
yes, it's harmless in this position but it provides no additional benefits to the select 1 idiom and is suggestive of poor query discipline. it's far easier to say just don't ever use select * in queries.
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RHSeeger 975 days ago
I would add to this a bit in that

1. Given that "select " is considered something to avoid except when necessary in edge cases

2. And "select 1" will accomplish the same goal

Anyone reading the "select " version of the code will have to stop and consider whether it is using "select " for a reason, because "select 1" would be the normal choice. Using "select " is assumed to be conveying some intent (that isn't there) _because_ it's not the expected way to do it.

I kind of see it like

    if (thisField == thatField) ...
vs

    if ( (( true || false )) && ( 11 == 11 ) && thisField == thatField ) ...
Sure, they do the same thing... but you have to stop and look at the second one to make sure you're understanding what it does and if there's some reason its weird.
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