“where 1=1” statement

Question

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?

Answer 1

In SQL, It's easier to make a generate a posh wherever statement if you do not need to compute if you are adding the primary condition or not, therefore usually a 1=1 is placed in the beginning, and every one alternative condition may be appended with an AND Syntax. 

Here, 1=1 will always be true. While debugging sometimes you observe people use  '1=1' at the top of a where condition as it allows them to freely change the rest of the conditions when they are debugging the query.

When you are adding and value=" Toyota" then you no need to worry about whether there is a condition before or just WHERE.

Have a look at the below example. 

QUERY:

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 will have to have a complicated set of logic like this:

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;