difference between if and if exists

Question

I have this stored procedure, I was wondering if "if exists" will actually compare the value returned by select statement or it will just check if that condition can be executed or not, sorry for such a stupid question but I am new to SQL,

declare @m_ID_v int set @m_ID_v = ( select ID_C from M_T where MName_C = @MName_parameter) declare @g bit if exists (select G_L_Column from G_L_table Where M_ID_Column = @M_ID_variable) set @g_v = 1 else set @g_variable = 0

my select statement

select G_L_Column from G_L_table Where M_ID_Column = @M_ID_variable

Is returning either true or false, so just wanna make sure if "if exists" will work as "if"

The block in if exists will execute if your select query inside it return at least 1 record, equal to if((select query).records.count > 0) — Ta Duy Anh
– Ta Duy Anh, Commented Oct 15, 2012 at 9:21
how can I use if statement then as it gives me error and I asked a question and they asked me to use "exists" stackoverflow.com/questions/12892194/… — Change
– Change, Commented Oct 15, 2012 at 9:26
@Ignacio - Saw you removed the other question. Just for what it's worth, I did not down-vote your question(s). — SchmitzIT
– SchmitzIT, Commented Oct 15, 2012 at 10:33
@user569711 I was getting negative votes without explanation so I had to remove it, but thanks for letting me know :) — Change
– Change, Commented Oct 15, 2012 at 10:52

Guffa · Accepted Answer · 2012-10-15 09:22:03Z

4

Using if exists is not working as if. It doesn't check if the returned value is true or false, it checks if there exists a value.

If your query always returns a value, the if exists will always evaluate to true.

answered Oct 15, 2012 at 9:22

Guffa

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2 Comments

Guffa Over a year ago

@Ignacio: If the select returns a bit, can't you simpy assign it to the variable?

Change Over a year ago

I can actually but for the moment I just checking it against a value which solved the problem, ta

Kapil Khandelwal · Accepted Answer · 2012-10-15 09:22:06Z

EXISTS (Transact-SQL)

Specifies a subquery to test for the existence of rows.

Returns TRUE if a subquery contains any rows.

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