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.
Is there difference in performance when querying someting like this?
Query 1:
SELECT * FROM Customer WHERE Name=Name
Query 2:
SELECT * FROM Customer
I will use it in conditional select all
SELECT * FROM Customer
WHERE Name = CASE WHEN #QueryAll='true' THEN Name ELSE #SearchValue END
If there's no performance issue in Query 1 and 2, I think it is a short code for this one:
IF #QueryAll='true'
SELECT * FROM Customer
ELSE
SELECT * FROM Customer WHERE Name=#SearchValue
You should read Dynamic Search Conditions in T‑SQL by Erland Sommarskog.
If you use SQL Server 2008 or later, then use OPTION(RECOMPILE) and write the query like this:
SELECT *
FROM Customer
WHERE
(Name = #SearchValue OR #QueryAll='true')
OPTION (RECOMPILE);
I usually pass NULL for #SearchValue to indicate that this parameter should be ignored, rather than using separate parameter #QueryAll. In this convention the query becomes this:
SELECT *
FROM Customer
WHERE
(Name = #SearchValue OR #SearchValue IS NULL)
OPTION (RECOMPILE);
Edit
For details see the link above. In short, OPTION(RECOMPILE) instructs SQL Server to recompile execution plan of the query every time it is run and SQL Server will not cache the generated plan. Recompilation also means that values of any variables are effectively inlined into the query and optimizer knows them.
So, if #SearchValue is NULL, optimizer is smart enough to generate the plan as if the query was this:
SELECT *
FROM Customer
If #SearchValue has a non-NULL value 'abc', optimizer is smart enough to generate the plan as if the query was this:
SELECT *
FROM Customer
WHERE (Name = 'abc')
The obvious drawback of OPTION(RECOMPILE) is added overhead for recompilation (usually around few hundred milliseconds), which can be significant if you run the query very often.
The query 2 would be faster with an index on name column, and you should specify just the fields you'll need, not all of them.
For some guidance in optional parameter queries, take a look here: Sometimes the Simplest Solution Isn't the Best Solution (The Optional Parameter Problem)
I have the following query in SQL Server 2005 which works fine:
DECLARE #venuename NVARCHAR(100)
DECLARE #town NVARCHAR(100)
SET #venuename = NULL -- normally these are parameters in the stored proc.
SET #town = 'London'
SELECT COUNT(*) FROM dbo.Venue
WHERE
(#VenueName IS NULL OR CONTAINS((Venue.VenueName), #VenueName))
AND
(#Town IS NULL OR Town LIKE #Town + '%')
It uses short-circuiting when null values are passed for the parameters (there are many more in the real SP than shown in my example).
However after upgrading to SQL 2012, running this query with NULL passed for #VenueName fails with the error "Null or empty full-text predicate" as SQL Server seems to be running (or evaluating) the CONTAINS statement for #VenueName even when #VenueName is set to NULL.
Is there a way to use short-circuiting in 2012 or is this no longer possible? I'd hate to have to rewrite all of my SPs as we've used this technique in dozens of stored procedures across multiple projects over the years.
I do not know much about sql 2012 but can you please try following
DECLARE #venuename NVARCHAR(100)
DECLARE #town NVARCHAR(100)
SET #venuename = '""' -- -- **Yes '""' instead of null**.
SET #town = 'London'
SELECT COUNT(*) FROM dbo.Venue
WHERE
(#VenueName ='""' OR CONTAINS((Venue.VenueName), #VenueName))
AND
(#Town IS NULL OR Town LIKE #Town + '%')
Check out this thread: OR Operator Short-circuit in SQL Server Within SQL server, there is no guarantee that an OR clause breaks early. It's always been that way, so I guess you've just been lucky that it worked with SQL Server 2005.
To workaround your problem, consider using the ISNULL function every time you supply a parameter value that might be NULL, to the CONTAINS function.
This is Perfect Answer.
Let's examine these two statements:
IF (CONDITION 1) OR (CONDITION 2)
..
IF (CONDITION 3) AND (CONDITION 4)
...
If CONDITION 1 is TRUE, will CONDITION 2 be checked?
If CONDITION 3 is FALSE, will CONDITION 4 be checked?
What about conditions on WHERE: does the SQL Server engine optimize all conditions in a WHERE clause? Should programmers place conditions in the right order to be sure that the SQL Server optimizer resolves it in the right manner?
ADDED:
Thank to Jack for link, surprise from t-sql code:
IF 1/0 = 1 OR 1 = 1
SELECT 'True' AS result
ELSE
SELECT 'False' AS result
IF 1/0 = 1 AND 1 = 0
SELECT 'True' AS result
ELSE
SELECT 'False' AS result
There is not raise a Divide by zero exception in this case.
CONCLUSION:
If C++/C#/VB has short-circuiting why can't SQL Server have it?
To truly answer this let's take a look at how both work with conditions. C++/C#/VB all have short circuiting defined in the language specifications to speed up code execution. Why bother evaluating N OR conditions when the first one is already true or M AND conditions when the first one is already false.
We as developers have to be aware that SQL Server works differently. It is a cost based system. To get the optimal execution plan for our query the query processor has to evaluate every where condition and assign it a cost. These costs are then evaluated as a whole to form a threshold that must be lower than the defined threshold SQL Server has for a good plan. If the cost is lower than the defined threshold the plan is used, if not the whole process is repeated again with a different mix of condition costs. Cost here is either a scan or a seek or a merge join or a hash join etc... Because of this the short-circuiting as is available in C++/C#/VB simply isn't possible. You might think that forcing use of index on a column counts as short circuiting but it doesn't. It only forces the use of that index and with that shortens the list of possible execution plans. The system is still cost based.
As a developer you must be aware that SQL Server does not do short-circuiting like it is done in other programming languages and there's nothing you can do to force it to.
I am passing in a comma-delimited list of values that I need to compare to the database
Here is an example of the values I'm passing in:
#orgList = "1123, 223%, 54%"
To use the wildcard I think I have to do LIKE but the query runs a long time and only returns 14 rows (the results are correct, but it's just taking forever, probably because I'm using the join incorrectly)
Can I make it better?
This is what I do now:
declare #tempTable Table (SearchOrg nvarchar(max) )
insert into #tempTable
select * from dbo.udf_split(#orgList) as split
-- this splits the values at the comma and puts them in a temp table
-- then I do a join on the main table and the temp table to do a like on it....
-- but I think it's not right because it's too long.
select something
from maintable gt
join #tempTable tt on gt.org like tt.SearchOrg
where
AYEAR= ISNULL(#year, ayear)
and (AYEAR >= ISNULL(#yearR1, ayear) and ayear <= ISNULL(#yearr2, ayear))
and adate = ISNULL(#Date, adate)
and (adate >= ISNULL(#dateR1, adate) and adate <= ISNULL(#DateR2 , adate))
The final result would be all rows where the maintable.org is 1123, or starts with 223 or starts with 554
The reason for my date craziness is because sometimes the stored procedure only checks for a year, sometimes for a year range, sometimes for a specific date and sometimes for a date range... everything that's not used in passed in as null.
Maybe the problem is there?
Try something like this:
Declare #tempTable Table
(
-- Since the column is a varchar(10), you don't want to use nvarchar here.
SearchOrg varchar(20)
);
INSERT INTO #tempTable
SELECT * FROM dbo.udf_split(#orgList);
SELECT
something
FROM
maintable gt
WHERE
some where statements go here
And
Exists
(
SELECT 1
FROM #tempTable tt
WHERE gt.org Like tt.SearchOrg
)
Such a dynamic query with optional filters and LIKE driven by a table (!) are very hard to optimize because almost nothing is statically known. The optimizer has to create a very general plan.
You can do two things to speed this up by orders of magnitute:
Play with OPTION (RECOMPILE). If the compile times are acceptable this will at least deal with all the optional filters (but not with the LIKE table).
Do code generation and EXEC sp_executesql the code. Build a query with all LIKE clauses inlined into the SQL so that it looks like this: WHERE a LIKE #like0 OR a LIKE #like1 ... (not sure if you need OR or AND). This allows the optimizer to get rid of the join and just execute a normal predicate).
Your query may be difficult to optimize. Part of the question is what is in the where clause. You probably want to filter these first, and then do the join using like. Or, you can try to make the join faster, and then do a full table scan on the results.
SQL Server should optimize a like statement of the form 'abc%' -- that is, where the wildcard is at the end. (See here, for example.) So, you can start with an index on maintable.org. Fortunately, your examples meet this criteria. However, if you have '%abc' -- the wildcard comes first -- then the optimization won't work.
For the index to work best, it might also need to take into account the conditions in the where clause. In other words, adding the index is suggestive, but the rest of the query may preclude the use of the index.
And, let me add, the best solution for these types of searches is to use the full text search capability in SQL Server (see here).
I'm using a sub-query to get results needed (multiple records returned), and I want to put those results in a single record returned.
When I run the sub-query on its own, it works, but once I use it as a sub query, it no longer works due to a syntax error.
The following code causes a syntax error
(Incorrect syntax near '='.)
declare #test varchar(1000)
set #test = ''
SELECT description, (SELECT #test = #test + FirstName
FROM EMP_tblEmployee
)select #test
FROM EMP_tblCrew
So essentially, the sub query
(SELECT #test = #test + FirstName
FROM EMP_tblEmployee
)select #test
returns "charliejohnjacob"
The main query
SELECT description FROM EMP_tblCrew
returns "janitor"
So I want it to say
janitor | charliejohnjacob
2 fields, 1 record.
Your query is not syntactically correct and the T-SQL parser has a nasty habit of not reporting an error quite accurately at times. This is a bit of a stab in the dark but try:
SELECT
description,
(SELECT FirstName + ' ' FROM EMP_tblEmployee FOR XML PATH('')) AS [Name Concat Result]
FROM EMP_tblCrew
That will fix one thing at least, though I'm not sure how SQL server feels about concatenating inline like that. You also risk overflowing the varchar(1000) if your table is of appreciable size. Even varchar 8000 isn't very much for this kind of query.
Try searching google for "SQL Concatenate rows into string". There are a number of useful solutions for this.
It looks like you also need to join the employee to the crew table, so that you dont get some cartesian product (usually not what is wanted).
Probably the easiest path involves using a recursive CTE (common table expression). A detailed example of that is at https://www.simple-talk.com/sql/t-sql-programming/concatenating-row-values-in-transact-sql/
Note, this basically requires that you have sql 2008.
Another path would be to create a user defined function that returned the concatenated values from the EMP_tblEmployee table. You could do this in 2005 or 2008.