"where 1=1" statement
MysqlSqlDatabaseMysql Problem Overview
> Possible Duplicate:
> Why would someone use WHERE 1=1 AND <conditions> in a SQL clause?
I saw some people use a statement to query a table in a MySQL database like the following:
select * from car_table where 1=1 and value="TOYOTA"
But what does 1=1
mean here?
Mysql Solutions
Solution 1 - Mysql
It's usually when folks build up SQL statements.
When you add and value = "Toyota"
you don't have to worry about whether there is a condition before or just WHERE. The optimiser should ignore it
No magic, just practical
Example Code:
commandText = "select * from car_table where 1=1";
if (modelYear <> 0) commandText += " and year="+modelYear
if (manufacturer <> "") commandText += " and value="+QuotedStr(manufacturer)
if (color <> "") commandText += " and color="+QuotedStr(color)
if (california) commandText += " and hasCatalytic=1"
Otherwise you would have to have a complicated set of logic:
commandText = "select * from car_table"
whereClause = "";
if (modelYear <> 0)
{
if (whereClause <> "")
whereClause = whereClause + " and ";
commandText += "year="+modelYear;
}
if (manufacturer <> "")
{
if (whereClause <> "")
whereClause = whereClause + " and ";
commandText += "value="+QuotedStr(manufacturer)
}
if (color <> "")
{
if (whereClause <> "")
whereClause = whereClause + " and ";
commandText += "color="+QuotedStr(color)
}
if (california)
{
if (whereClause <> "")
whereClause = whereClause + " and ";
commandText += "hasCatalytic=1"
}
if (whereClause <> "")
commandText = commandText + "WHERE "+whereClause;
Solution 2 - Mysql
If that query is being built dynamically, original author probably doesn't want to consider an empty set of conditions, so ends with something like this:
sql = "select * from car_table where 1=1"
for each condition in condition_set
sql = sql + " and " + condition.field + " = " + condition.value
end
Solution 3 - Mysql
1=1
will always be true, so the value="TOYOTA"
bit is the important one.
You get this in a few scenarios including:
Generated SQL: It's easier to create a generate a complex where
statement if you don't have to work out if you're adding the first condition or not, so often a 1=1
is put at the beginning, and all other conditions can be appended with an And
Debugging: Sometimes you see people put in a 1=1
at the top of a where condition as it enables them to freely chop and change the rest of the conditions when debugging a query. e.g.
select * from car_table
where 1=1
--and value="TOYOTA"
AND color="BLUE"
--AND wheels=4
It has to be said that it isn't particularly good practice and normally shouldn't occur in production code. It may even not help the optimization of the query very much.
Solution 4 - Mysql
As well as all the other answers, it's a simple technique for SQL injection attacks. If you add a OR where 1=1
statement to some SQL then it's going to return all the results due to the inherent truthiness of the expression.
Solution 5 - Mysql
Its just an always true expression. Some people use it as an work-around.
They have a static statement like:
select * from car_table where 1=1
So they can now add something to the where clause with
and someother filter
Solution 6 - Mysql
the 1=1 where condition is always true because always 1 is equal 1 , so this statement will be always true. While it means nothing sometimes. but other times developers uses this when the where condition is generated dynamically.
for example lets see this code
<?php
//not that this is just example
//do not use it like that in real environment because it security issue.
$cond = $_REQUEST['cond'];
if ($cond == "age"){
$wherecond = " age > 18";
}
$query = "select * from some_table where $wherecond";
?>
so in the above example if the $_REQUEST['cond'] is not "age" the query will return mysql error because there are nothing after the where condition.
the query will be select * from some_table where and that is error
to fix this issue (at least in this insecure example) we use
<?php
//not that this is just example
//do not use it like that in real environment because it security issue.
$cond = $_REQUEST['cond'];
if ($cond == "age"){
$wherecond = " age > 18";
} else {
$wherecond = " 1=1";
}
$query = "select * from some_table where $wherecond";
?>
so now if the $_REQUEST['cond'] is not age the $wherecond will be 1=1 so the query will not have mysql error return.
the query will be select * from some_table where 1=1 and that avoid the mysql error
hope you understand when we use 1=1 while note that the above example is not real world example and it just to show you the idea.
Solution 7 - Mysql
Most of time developer use these type of query if he is developing a query builder type application or building some complex SQL query so along with the select statement string add a conditional clause Where 1=1, and in program no need to add any check for it.
Solution 8 - Mysql
The query finds all rows for which 1 equals 1 and value equals 'TOYOTA'. So in this case it's useless, but if you omit a WHERE statement, it can be a good idea to use WHERE 1=1 to remind you that you chose NOT to use a WHERE clause.
Solution 9 - Mysql
the use of this comes in complex queries when passing conditions dynamically,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.
no need to use 1=1 you can use 0=0 2=2,3=3,5=5 25=25 ......
select * from car_table where 0=0 and value="TOYOTA"
here also you will get the same result like 1=1 condition
because all these case is always true expression
1=1 is alias for true
Solution 10 - Mysql
i did this when i need to apply the filters dynamically.
like, while coding i dunno how many filter user will apply (fld1 = val1 and fld2=val2 and ...)
so, to repeat the statement "and fld = val" i start with "1 = 1".
hence, i need not trim the first "and " in the statement.