Question

I have an interesting result and don’t understand why.

SELECT * 
  FROM items im
 WHERE ItemNumber

ItemNumber is a varchar(50).

The results of this query is returning all items that the ItemNumber starts with a number. If the ItemNumber begins with a letter, it is excluded.

Does anyone have an explanation why the query interacts in this way?

Answer 1

MYSQL will return all rows with the ItemNumber starts with a number which is greater than equal to 0.5 and less than equal to -0.5. It consider all number greater >= +/-0.5 as true. And where clause works based on true or false only.

true >= -0.5  > false < 0.5 <= true

Very smartly, mysql consider All >= +/-0.5 number as 1 (true). It takes true for rounded non-zero values.

IF you write

SELECT * FROM items im WHERE 1; // will return all rows.
SELECT * FROM items im WHERE 0.5; // will return all rows.
SELECT * FROM items im WHERE 0.4; // will return nothing.
SELECT * FROM items im WHERE 1 and 0.2; // will return nothing.
SELECT * FROM items im WHERE 0.3 or 0.5; // will return all rows.