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

Question

Why would someone use WHERE 1=1 AND <conditions> in a SQL clause (Either SQL obtained through concatenated strings, either view definition)

I've seen somewhere that this would be used to protect against SQL Injection, but it seems very weird.

If there is injection WHERE 1 = 1 AND injected OR 1=1 would have the same result as injected OR 1=1.

Later edit: What about the usage in a view definition?

---

Thank you for your answers.

Still, I don't understand why would someone use this construction for defining a view, or use it inside a stored procedure.

Take this for example:

CREATE VIEW vTest AS
SELECT FROM Table WHERE 1=1 AND table.Field=Value

Stairwell

"why would someone use this construction for defining a view" Probably out of habit. It offers no functional advantage in static queries. – Rabbin

Nobody should use Dynamic SQL – Shafting

Answer 1

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.

Jagged

There have been instances in the past of SQL Server generate poor plans when this technique is used. For that reason, I no longer use it, unless the query is targeted at retrieving schema definition. – Crymotherapy

Agreed. Vote up for answering the question, but I'd recommend coding the query properly to begin with rather than being lazy. – Joyous

Sometimes is not about being lazy, but having a cleaner code. – Repetition

dealing with trailing ANDs or COMMAs isn't dirty... nothing is cleaner by having 1=1 all over your SQL. – Jake

Yeah, if our DBAs saw that query coming up in their RUNSTATS statistics collections, they'd hunt you down like a duck (and before anyone asks, that's actually a humorous line from the 'Back to the future' movies). – Inestimable

DBAs? What are they for? :) – Repetition

DBA's are there to clean up after programmers who think they know how to use databases effectively. – Feuilleton

One place where this technique is very useful is with BI tools that allow you to place "conditional prompts" in SQL, such as Microstrategy. – Chatham

"Lazy" I like to think it's smart, not lazy. You're avoiding repetitive code and unnecessary condition checks. Without being able to add where 1=1 (Oracle) or where true (Postgres), I will have to check for each condition whether it is the first one. There is no point in doing so, and it only adds more boilerplate code. – Rabbin

I am all for either way, and if someone can improve the performance, the better. I just wanted to point out that building an array of conditions (stored as strings) and then joining them with an "and" can be just as lazy of an alternative to the 1=1 approach. – Keyway

Can WHERE 1 AND <conditions> pattern introduces giant security holes via sql injection in any way vs WHERE <condition 1> AND <conditions 2+>? My superior is telling me it does introduce sql injection, its atrocious and shouldn't be done. They also can't give me any examples. Are they crazy and mistaking this for the OR 1=1 injection? – Phoebephoebus

@radtek: No, SQL injection has nothing to do with the actual SQL statements used. It's all about how the SQL statements are called. – Jagged

That's what I thought, I don't see any security holes with that. In both cases, if the function that generates the SQL allows for no conditions, we are selecting everything in that table. – Phoebephoebus

and shouldn't the execution plan be the exact same, with or without the condition? So I don't see any harm in using this; it allows for cleaner code and the execution is the same. – Pipsissewa

How about putting the 1 = 1 at the end and using <condition> AND? Wouldn't this solve the poor query plan issue? I wouldn't be surprised if the first conditions have more impact than those coming after ... – Chaulmoogra

On SQL Server this does not generate performance overhead thanks to Constant Folding and Expression Evaluation (learn.microsoft.com/en-us/sql/relational-databases/…). – Bivens

Laziness is the root of all evil – Shafting

Now, this has been a while, but a long time ago I had to build code that would build SQL queries for a VB6 application. It's easier than you think to solve this programmatically. Just put the and in all of the conditions and after concatenation, remove first and. First time I've seen this 1 = 1 has been recently when reviewing code from other developers in native queries that had no need for building the where clause, which is really weird. That's how I found this question. I was looking for why would anybody do that before asking a dev to remove it from their code... – Jemmie

Answer 2

Just adding a example code to Greg's answer:

dim sqlstmt as new StringBuilder
sqlstmt.add("SELECT * FROM Products")
sqlstmt.add(" WHERE 1=1") 

''// From now on you don't have to worry if you must 
''// append AND or WHERE because you know the WHERE is there
If ProductCategoryID <> 0 then
  sqlstmt.AppendFormat(" AND ProductCategoryID = {0}", trim(ProductCategoryID))
end if
If MinimunPrice > 0 then
  sqlstmt.AppendFormat(" AND Price >= {0}", trim(MinimunPrice))
end if

Repetition

bit hacky, but seems like a valid use. – Consternation

This should be the accepted answer. The practice is really only hack around to not having to determine how many conditionals you have. – Vagrancy

Answer 3

I've seen it used when the number of conditions can be variable.

You can concatenate conditions using an " AND " string. Then, instead of counting the number of conditions you're passing in, you place a "WHERE 1=1" at the end of your stock SQL statement and throw on the concatenated conditions.

Basically, it saves you having to do a test for conditions and then add a "WHERE" string before them.

Gloria

Answer 4

Seems like a lazy way to always know that your WHERE clause is already defined and allow you to keep adding conditions without having to check if it is the first one.

Plausive

"Lazy" I like to think it's smart, not lazy. You're avoiding repetitive code and unnecessary condition checks. Without being able to add where 1=1 (Oracle) or where true (Postgres), I will have to check for each condition whether it is the first one. There is no point in doing so, and it only adds more boilerplate code. – Rabbin

@Rabbin Writing code is often - if not mostly - about handling different conditions. This is just another condition that needs to be handled, which I personally think is lazy to pollute generated SQL with. If you architect your code to add 'Where 1 = 1' in ONE place, you could - with little extra effort - handle the difference between zero and many conditions in that ONE place in your code. My guess is though, advocates for 'Where 1 = 1' sprinkle it throughout their codebase, which brings me to the conclusion laziness breeds laziness. – Complexion

@JasonS Laziness is the father of Invention. – Rabbin

@Rabbin I'm lazy because I don't like to update code in hundreds of places, so the invention is put it in one place. To me WHERE 1=1 breeds the extra work of maintaining the same code in multiple places and reading it in all your generated SQL. I'm lazier than you I think! – Complexion

Answer 5

Indirectly Relevant: when 1=2 is used:

CREATE TABLE New_table_name 
as 
select * 
FROM Old_table_name 
WHERE 1 = 2;

this will create a new table with same schema as old table. (Very handy if you want to load some data for compares)

Porush

Forgot to add, while it will create a new table with same data as old, the new table wont have other constraints like foreign key from older table – Porush

Answer 6

I found this pattern useful when I'm testing or double checking things on the database, so I can very quickly comment other conditions:

CREATE VIEW vTest AS
SELECT FROM Table WHERE 1=1 
AND Table.Field=Value
AND Table.IsValid=true

turns into:

CREATE VIEW vTest AS
SELECT FROM Table WHERE 1=1 
--AND Table.Field=Value
--AND Table.IsValid=true

Craal

Answer 7

1 = 1 expression is commonly used in generated sql code. This expression can simplify sql generating code reducing number of conditional statements.

Undertake

Answer 8

Actually, I've seen this sort of thing used in BIRT reports. The query passed to the BIRT runtime is of the form:

select a,b,c from t where a = ?

and the '?' is replaced at runtime by an actual parameter value selected from a drop-down box. The choices in the drop-down are given by:

select distinct a from t
union all
select '*' from sysibm.sysdummy1

so that you get all possible values plus "*". If the user selects "*" from the drop down box (meaning all values of a should be selected), the query has to be modified (by Javascript) before being run.

Since the "?" is a positional parameter and MUST remain there for other things to work, the Javascript modifies the query to be:

select a,b,c from t where ((a = ?) or (1==1))

That basically removes the effect of the where clause while still leaving the positional parameter in place.

I've also seen the AND case used by lazy coders whilst dynamically creating an SQL query.

Say you have to dynamically create a query that starts with select * from t and checks:

• the name is Bob; and
• the salary is > $20,000

some people would add the first with a WHERE and subsequent ones with an AND thus:

select * from t where name = 'Bob' and salary > 20000

Lazy programmers (and that's not necessarily a bad trait) wouldn't distinguish between the added conditions, they'd start with select * from t where 1=1 and just add AND clauses after that.

select * from t where 1=1 and name = 'Bob' and salary > 20000

Inestimable

"Lazy" I like to think it's smart, not lazy. You're avoiding repetitive code and unnecessary condition checks. Without being able to add where 1=1 (Oracle) or where true (Postgres), I will have to check for each condition whether it is the first one. There is no point in doing so, and it only adds more boilerplate code. – Rabbin

@ADTC, I didn't mean lazy in a bad way. In fact, lazy is a good trait in programming :-) I'll clarify. – Inestimable

Laziness is the root of all evil – Shafting

Answer 9

where 1=0, This is done to check if the table exists. Don't know why 1=1 is used.

Crashaw

Seen this used to return an empty resultset from the database to be used as a holder for new records. – Symmetrize

Answer 10

While I can see that 1=1 would be useful for generated SQL, a technique I use in PHP is to create an array of clauses and then do

implode (" AND ", $clauses);

thus avoiding the problem of having a leading or trailing AND. Obviously this is only useful if you know that you are going to have at least one clause!

Matrass

That's where the 1=1 comes in. It gives you that "at least one clause" so you don't have to worry about just slapping on an " AND abc" – Gloria

I like this idea! See here for more complete example #35326660 – Sapphire

Answer 11

Here's a closely related example: using a SQL MERGE statement to update the target tabled using all values from the source table where there is no common attribute on which to join on e.g.

MERGE INTO Circles
   USING 
      (
        SELECT pi
         FROM Constants
      ) AS SourceTable
   ON 1 = 1
WHEN MATCHED THEN 
  UPDATE
     SET circumference = 2 * SourceTable.pi * radius;

Scapula

Answer 12

Why would someone use WHERE 1=1 AND <proper conditions>

I've seen homespun frameworks do stuff like this (blush), as this allows lazy parsing practices to be applied to both the WHERE and AND Sql keywords.

For example (I'm using C# as an example here), consider the conditional parsing of the following predicates in a Sql query string builder:

var sqlQuery = "SELECT * FROM FOOS WHERE 1 = 1"
if (shouldFilterForBars)
{
    sqlQuery = sqlQuery + " AND Bars > 3";
}
if (shouldFilterForBaz)
{
    sqlQuery = sqlQuery + " AND Baz < 12";
}

The "benefit" of WHERE 1 = 1 means that no special code is needed:

• For AND - whether zero, one or both predicates (Bars and Baz's) should be applied, which would determine whether the first AND is required. Since we already have at least one predicate with the 1 = 1, it means AND is always OK.
• For no predicates at all - In the case where there are ZERO predicates, then the WHERE must be dropped. But again, we can be lazy, because we are again guarantee of at least one predicate.

This is obviously a bad idea and would recommend using an established data access framework or ORM for parsing optional and conditional predicates in this way.

Rayraya

Or if rolling your own, the where clause builder should be in one place in your code. Then you can handle zero predicates or more than zero predicates in a single location in your code. My suspicion is that the existence of WHERE 1=1 is a fair indicator that that is NOT the case, that the code base is littered with bits of strings WHERE 1=1, which would indicate to me an application architecture problem, and I would guess not the only one! – Complexion

Actually there's nothing "bad" about the idea, much less an "obvious" fault. Nor is an ORM the proper way at all cases. Learn SQL and Relational Algebra people... – Lynd

Answer 13

If you came here searching for WHERE 1, note that WHERE 1 and WHERE 1=1 are identical. WHERE 1 is used rarely because some database systems reject it considering WHERE 1 not really being boolean.

Parotitis

Answer 14

Having review all the answers i decided to perform some experiment like

SELECT
*
FROM MyTable

WHERE 1=1

Then i checked with other numbers

WHERE 2=2
WHERE 10=10
WHERE 99=99

ect Having done all the checks, the query run town is the same. even without the where clause. I am not a fan of the syntax

Turnover

Answer 15

This is useful in a case where you have to use dynamic query in which in where clause you have to append some filter options. Like if you include options 0 for status is inactive, 1 for active. Based from the options, there is only two available options(0 and 1) but if you want to display All records, it is handy to include in where close 1=1. See below sample:

Declare @SearchValue    varchar(8) 
Declare @SQLQuery varchar(max) = '
Select [FirstName]
    ,[LastName]
    ,[MiddleName]
    ,[BirthDate]
,Case
    when [Status] = 0 then ''Inactive''
    when [Status] = 1 then ''Active''
end as [Status]'

Declare @SearchOption nvarchar(100)
If (@SearchValue = 'Active')
Begin
    Set @SearchOption = ' Where a.[Status] = 1'
End

If (@SearchValue = 'Inactive')
Begin
    Set @SearchOption = ' Where a.[Status] = 0'
End

If (@SearchValue = 'All')
Begin
    Set @SearchOption = ' Where 1=1'
End

Set @SQLQuery = @SQLQuery + @SearchOption

Exec(@SQLQuery);

Tush

Answer 16

Saw this in production code and asked seniors for help.

Their answer:

-We use 1=1 so when we have to add a new condition we can just type

and <condition>

and get on with it.

Affianced

Answer 17

I do this usually when I am building dynamic SQL for a report which has many dropdown values a user can select. Since the user may or may not select the values from each dropdown, we end up getting a hard time figuring out which condition was the first where clause. So we pad up the query with a where 1=1 in the end and add all where clauses after that.

Something like

select column1, column2 from my table where 1=1 {name} {age};

Then we would build the where clause like this and pass it as a parameter value

string name_whereClause= ddlName.SelectedIndex > 0 ? "AND name ='"+ ddlName.SelectedValue+ "'" : "";

As the where clause selection are unknown to us at runtime, so this helps us a great deal in finding whether to include an 'AND' or 'WHERE'.

Hushaby

Answer 18

Making "where 1=1" the standard for all your queries also makes it trivially easy to validate the sql by replacing it with where 1 = 0, handy when you have batches of commands/files.

Also makes it trivially easy to find the end of the end of the from/join section of any query. Even queries with sub-queries if properly indented.

Alvera

Answer 19

I first came across this back with ADO and classic asp, the answer i got was: performance. if you do a straight

Select * from tablename

and pass that in as an sql command/text you will get a noticeable performance increase with the

Where 1=1

added, it was a visible difference. something to do with table headers being returned as soon as the first condition is met, or some other craziness, anyway, it did speed things up.

Amblygonite

If that's true, why doesn't the DBMS always add that? – Adhere

I have seen this as well, but sorry I cannot specify the engine / version. It was a at some point in my 20+ years of sql coding. I think what was happening is the that without any Where clause, the execution plan ended up doing a table scan; adding where 1 =1 resulted in a better plan. But the plural of anecdote <> data; i can't swear the underlying issue wasn't a transient network or other resource problem :-p – Alvera

Answer 20

Using a predicate like 1=1 is a normal hint sometimes used to force the access plan to use or not use an index scan. The reason why this is used is when you are using a multi-nested joined query with many predicates in the where clause where sometimes even using all of the indexes causes the access plan to read each table - a full table scan. This is just 1 of many hints used by DBAs to trick a dbms into using a more efficient path. Just don't throw one in; you need a dba to analyze the query since it doesn't always work.

Sequence

Do you have any citations that document this behavior for some databases? – Mellissamellitz

Answer 21

Here is a use case... however I am not too concerned with the technicalities of why I should or not use 1 = 1. I am writing a function, using pyodbc to retrieve some data from SQL Server. I was looking for a way to force a filler after the where keyword in my code. This was a great suggestion indeed:

if _where == '': _where = '1=1'
...
...
...
cur.execute(f'select {predicate} from {table_name} where {_where}')

The reason is because I could not implement the keyword 'where' together inside the _where clause variable. So, I think using any dummy condition that evaluates to true would do as a filler.

Sidewheel