The role of where 1=1 in SQL statements _ database other

Looking at the program from time to time, found that the basic as long as a patchwork of SQL statements, basically will write:
where 1 = 1

Internet search for the next reason: Can not determine where there is a statement after the time to add 1=1, when there are no other conditional statements, and 1=1, you will not lose the wrong.

PS: I understand that the following judgment statement is convenient to add and id=8 and cid=9 some judgments, do not judge whether the select * from table there is no where, I understand, know the friend, can say, thank you