Related
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
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.
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
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.
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.
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)
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
1 = 1 expression is commonly used in generated sql code. This expression can simplify sql generating code reducing number of conditional statements.
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
where 1=0, This is done to check if the table exists. Don't know why 1=1 is used.
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!
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;
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.
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.
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
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);
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.
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'.
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.
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.
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.
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.
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
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.
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
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.
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.
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)
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
1 = 1 expression is commonly used in generated sql code. This expression can simplify sql generating code reducing number of conditional statements.
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
where 1=0, This is done to check if the table exists. Don't know why 1=1 is used.
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!
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;
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.
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.
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
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);
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.
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'.
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.
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.
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.
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.
I have a query that joins some tables and when I use = operator instead of in operator in a where clause like this I get a significant performance improvement.
= operator takes less than a second.
in operator takes about a minute.
where P.GID in ( SELECT GID from [dbo].[fn_SomeFunction] (15268) )
the sub query returns 1 result in most of the cases and just this change will improve most of the cases but will cause errors for some other cases.
any ideas why this behavior?
Try something like that it is not tested and may contain some syntactic errors.
The main idea is to get the desired ids in a temp table variable and use that in a join.
Hope that helps.
DECLARE #gids TABLE(
GID UNIQUEIDENTIFIER NOT NULL
)
INSERT INTO #gids (GID)
SELECT
GID
FROM [dbo].[fn_SomeFunction](15268)
SELECT * FROM SomeTable st INNER JOIN st.GID = #gids.GID
If that truly represents a functions that is what is killing your execution time. You can verify this by looking at the execution plan.
What happens is that in your subquery that function has to be calculated over and over again. If you can remove the function and replace with a query you should notice an improvement.
Additionally, if the functions return type doesn't match the column's type there will need to be an implicit conversion done on each return item. Changing the functions return type(or the columns type) to match would also help performance.
DateTime <> smalldatetime for example and requires an implicit conversion.
I have a query here and I'm curious if there is a shorter way of writing this query, meaning to reduce the query from using an IF argument to determine if it should use the param or not in the statement. Please see below:
#Param varchar(10) = NULL
IF #Param IS NOT NULL
BEGIN
SELECT * FROM TABLE WHERE Column = #Param
END
ELSE
BEGIN
SELECT * FROM TABLE
END
Could this be reduced to one simple query instead like this?
#Param varchar(10) = NULL
SELECT * FROM TABLE WHERE Column = COALESCE( Any, #Param )
I looked at Coalesce, but didn't see if I could use an Any sort of feature. I hope this makes sense.
Question is how to acheive this. Second question is which would be better on performance?
There is no any style command, but if you use the #Param first and then the value in the column itself, that should work...
SELECT * FROM TABLE WHERE Column = COALESCE(#Param, Column)
If #Param is Null then it is ignored and the next item in the list is used.
You can also use IsNull to do the same thing...
SELECT * FROM TABLE WHERE Column = ISNULL(#Param, Column)
To answer the 2nd part of the question, my feeling is that using a separate statement will always be more efficient. The condensed version might be less code, but isn't necessarily easier to understand or quicker to run.
I have an SQL query that takes these parameters:
#SearchFor nvarchar(200) = null
,#SearchInLat Decimal(18,15) = null
,#SearchInLng Decimal(18,15) = null
,#SearchActivity int = null
,#SearchOffers bit = null
,#StartRow int
,#EndRow int
The variables #SearchFor, #SearchActivity, #SearchOffers can be either null or not null. #SearchInLat and #SearchInLng must both null, or both have values.
I'm not going to post the whole query as its boring and hard to read, but the WHERE clause is shaped like this:
( -- filter by activity --
(#SearchActivity IS NULL)
OR (#SearchActivity = Activities.ActivityID)
)
AND ( -- filter by Location --
(#SearchInLat is NULL AND #SearchInLng is NULL)
OR ( ... )
)
AND ( -- filter by activity --
#SearchActivity is NULL
OR ( ... )
)
AND ( -- filter by has offers --
#SearchOffers is NULL
OR ( ... )
)
AND (
... -- more stuff
)
I have read that this is a bad way to structure a query - that SqlServer has trouble working out an efficient execution plan with lots of clauses like this, so I'm looking for other ways to do it.
I see two ways of doing this:
Construct the query as a string in my client application, so that the WHERE clause only contains filters for the relevant parameters. The problem with this is it means not accessing the database through stored procedures, as everything else is at the moment.
Change the stored procedure so that it examines which arguments are null, and executes child procedures depending on which arguments it is passed. The problem here is that it would mean repeating myself a lot in the definition of the procs, and thus be harder to maintain.
What should I do? Or should I just keep on as I am currently doing? I have OPTION (RECOMPILE) set for the procedures, but I've heard that this doesn't work right in Server 2005. Also, I plan to add more parameters to this proc, so I want to make sure whatever solution I have is fairly scaleable.
The answer is to use DynamicSQL (be it in the client, or in an SP using sp_executesql), but the reason why is long, so here's a link...
Dynamic Search Conditions in T-SQL
A very short version is that one-size does not fit all. And as the optimiser creates one plan for one query, it's slow. So the solution is to continue using parameterised queries (for execution plan caching), but to have many queries, for the different types of search that can happen.
Perhaps an alternative might be to perform several separate select statements?
e.g.
( -- filter by activity --
if #SearchActivity is not null
insert into tmpTable (<columns>)
select *
from myTable
where (#SearchActivity = Activities.ActivityID)
)
( -- filter by Location --
if #SearchInLat is not null and #SearchInLng is not null
insert into tmpTable (<columns>)
select *
from myTable
where (latCol = #SearchInLat AND lngCol = #SearchInLng)
etc...
then select the temp table to return the final result set.
I'm not sure how this would work with respect to the optimiser and the query plans, but each individual select would be very straightforward and could utilise the indexes that you would have created on each column which should make them very quick.
Depending on your requirements it also may make sense to create a primary key on the temp table to allow you to join to it on each select (to avoid duplicates).
Look at the performance first, like others have said.
If possible, you can use IF clauses to simplify the queries based on what parameters are provided.
You could also use functions or views to encapsulate some of the code if you find you are repeating it often.