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.
The following query on my oracle db gives results that look fine when run in SQL Developer.
select *
from guideline$ a left outer join textfragment$ t
on (a.TEXTFRAGMENT_CODE = t.TEXTFRAGMENT$_CODE)
start with a.knowledge$_Code = 71122 and a.guideline$_pcode is null
connect by prior a.guideline$_Code = a.guideline$_pcode
order SIBLINGS by a.tag_order
All rows are populated correctly. When the same exact query is ran in my program using OleDbReader.ExecuteReader() some of the rows contain a null value for a specific column when they didn't in my SQL Developer results. The data type of that column is CLOB. I can not see any pattern as to why some of the rows have a null value and some do not.
Not sure what other information would be helpful...
Does anyone have any ideas on what might be going on?
Your problem may be related to the way that binary data is retrieved with OleDbDataReader.
You should use GetBytes(), and follow this article.
I am working ServiceStack.OrmLite using MS SQL Server. I would like to execute raw SQL against database but original documentation contains description of how to do it with SELECT statement only. That is not enough for me.
I cant find the way to run anything as simple as that:
UPDATE table1
SET column1 = 'value1'
WHERE column2 = value2
Using, for example:
var two = db.Update(#"UPDATE table1
SET column1 = 'value1'
WHERE column2 = value2");
Running this expressions with db.Update() or db.Update<> produces uncomprehensive errors like
Incorrect syntax near the keyword 'UPDATE'.
I would like to use raw sql because my real UPDATE expression uses JOIN.
db.Update is for updating a model or partial model as shown in OrmLite's Documentation on Update. You can choose to use the loose-typed API to build your update statement, e.g:
db.Update(table: "table1",
set: "column1 = {0}".Params("value1"),
where: "column2 = {0}".Params("value2"));
The Params extension method escapes your values for you.
Otherwise the way to execute any arbitrary raw sql is to use db.ExecuteSql().
If it is a SELECT statement and you want to execute using raw sql you can use:
List<Person> results = db.SqlList<Person>("SELECT * FROM Person WHERE Age < #age", new { age=50});
Reference: https://github.com/ServiceStack/ServiceStack.OrmLite#typed-sqlexpressions-with-custom-sql-apis
I am new with the linq and i need to do this query with linq in vb.net from a data table
Every column are setted to VAR CHAR if its useful for the query:
SELECT Sum(IIf([ColumnNameToCountValues] IN
('value1','value2','value3')
And [EmployeId] Like '[IDvalue]'
And [PROJECT] LIKE '[ProjectName]',1,0))
AS Total FROM [DatatableName];
This query should return an integer.
where are your error and what are your question also what have you tried? From what you have said "This query should return an integer." May be your output got error, isn't it?
So, why not just change your database column data type to INT
I need to extract all records which have a field which does NOT have a unique value.
I can't figure out an elegant way to do it - using annotation or some other way. I see a "value_annotate" method to the object manager but it's unclear if it's at all related.
Currently I'm using the inelegant way of simple looping through all values and doing a get on the value, and if there's an exception it means it's not unique..
Thanks
I can't say much about the Django part, but the query would look something like:
SELECT *
FROM foo
WHERE id IN (
SELECT MAX(id)
FROM foo
GROUP BY bar
HAVING COUNT(*)=1)
This will return all records where the "bar" field is unique.
I'd go direct to a raw query in this case. This'll look something like the following, assuming you're using Django 1.2:
query = """
SELECT *
FROM table
GROUP BY field
HAVING COUNT(*) > 1
"""
non_uniques = Table.objects.raw(query)
For earlier than 1.2, see the django docs on raw queries