Why Would a SQL Query Have "Where 1 = 1"

What is the purpose of using WHERE 1=1 in SQL statements?

Yeah, it's typically because it starts out as 'where 1 = 0', to force the statement to fail.

It's a more naive way of wrapping it up in a transaction and not committing it at the end, to test your query. (This is the preferred method).

Why would someone use WHERE 1=1 AND conditions in a SQL clause?

If the list of conditions is not known at compile time and is instead built at run time, you don't have to worry about whether you have one or more than one condition. You can generate them all like:

and <condition>

and concatenate them all together. With the 1=1 at the start, the initial and has something to associate with.

I've never seen this used for any kind of injection protection, as you say it doesn't seem like it would help much. I have seen it used as an implementation convenience. The SQL query engine will end up ignoring the 1=1 so it should have no performance impact.

Why would a sql query have where 1 = 1

Was it dynamic queries? Sometimes that's helpful when building dynamic queries based on parameters that are optional.

Why the (1=1) in the Where clause?

When generating dynamic SQL from code, it can be useful to just start with a WHERE (1=1) then concatenate\append AND <Condition> as needed. Not sure if that's the case with that answer, but perhaps it was based on some code for generating SQL.

why would you use WHERE 1=0 statement in SQL?

A query like this can be used to ping the database. The clause:

WHERE 1=0

Ensures that non data is sent back, so no CPU charge, no Network traffic or other resource consumption.

A query like that can test for:

• server availability
• CUST_ATTR49 table existence
• ID column existence
• Keeping a connection alive
• Cause a trigger to fire without changing any rows (with the where clause, but not in a select query)
• manage many OR conditions in dynamic queries (e.g WHERE 1=0 OR <condition>)

where 1=1 statement

It's usually when folks build up SQL statements.

When you add and value = "Toyota" you don't have to worry about whether there is a condition before or just WHERE. The optimiser should ignore it

No magic, just practical

---

Example Code:

commandText = "select * from car_table where 1=1";

if (modelYear <> 0)     commandText += " and year="+modelYear
if (manufacturer <> "") commandText += " and value="+QuotedStr(manufacturer)
if (color <> "")        commandText += " and color="+QuotedStr(color)
if (california)         commandText += " and hasCatalytic=1"

Otherwise you would have to have a complicated set of logic:

commandText = "select * from car_table"
whereClause = "";
if (modelYear <> 0)
{
   if (whereClause <> "") 
      whereClause = whereClause + " and ";
   commandText += "year="+modelYear;
}
if (manufacturer <> "")
{    
   if (whereClause <> "") 
      whereClause = whereClause + " and ";
   commandText += "value="+QuotedStr(manufacturer)
}
if (color <> "")
{
   if (whereClause <> "") 
      whereClause = whereClause + " and ";
   commandText += "color="+QuotedStr(color)
}
if (california)
{
   if (whereClause <> "") 
      whereClause = whereClause + " and ";
   commandText += "hasCatalytic=1"
}

if (whereClause <> "")
   commandText = commandText + "WHERE "+whereClause;

why we are using 1 = 1 in SQL select Query

Tools often use this to let them append AND some_other_condition to the query, without having to worry whether this is the first predicate or not.

If you write

SELECT * FROM A

...and want to add a predicate you need to append "WHERE C1=1", but then adding a second predicate would append "AND C2=1"

But if you write

SELECT * FROM A WHERE 1=1

...you can just append "AND C1=1" for the first, and "AND C2=1" for the second

Why would Where 1 1 in a query return all rows?

It definitely looks like a bug in the view merging code of the Oracle optimizer. I bet you only get this with views which contain outer joins. Your ORDER BY solves it, because it practically forces a NO_MERGE on the view.

I wouldn't put either an ORDER BY or a NO_MERGE hint inside the view though, because (depending on your data volume) it could degrade performance of other queries which use the view. You should put a no_merge hint in the outer query:

Select /*+ NO_MERGE(foo) */ *
From foo
where
    1 <> 1

You should also raise an SR with Oracle support, as this is definitely a bug. That query should never ever return any rows no matter what you are selecting from, or how complex it is inside. Never ever.

I couldn't reproduce it, so it's probably fixed in the version I'm using. What's the db version you are using?

What does WHERE 1 mean in SQL?

It doesn't. It means ALWAYS TRUE so it won't have any filtering impact on your query. Query planner will probably ignore that clause.

It's usually used when you build a client side query by concatenating filtering conditions.

So, if your base query is stored in a string like this (example is in PHP, but it certainly applies to many other languages):

$sql = "select * from foo where 1 ";

Then you can just concatenate a lot of filtering conditions with an AND clause regardless of it being the first condition you are using or not:

// pseudo php follows...
if ($filter_by_name) {
    $sql = $sql . " and name = ? ";
}
if ($filter_by_number) {
    $sql = $sql . " and number = ? ";
}
// so on, and so forth.

---

Related Topics