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.

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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

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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.

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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.

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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)

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

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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

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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

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

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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!

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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;

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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.

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Why would someone use WHERE 1=1 AND

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.

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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

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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);

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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.

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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'.

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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.

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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.

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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.

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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.

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