mysql - How to JOIN two tables when not using any Primary Keys? -

i'm trying join 2 tables using columns aren't either of tables respective primary keys:

select * tablea inner join tableb b on a.col5 = b.col5 

yet above returning 0 results though know sure there rows in table a col5 values match values in col5 of table b.

what doing wrong?

you query:

select * tablea inner join tableb b on a.col5 = b.col5; 

has correct syntax join. if there matching values, return it. (or course, calling application , there errors either in application code or connection database, issue.)

some cases values same not:

• both values floats. same when printed out. bit @ end of value differs. never use floats equi-joins.
• one value number , other value string. conversion of 1 of values results in different value.
• one value date/time , other string. conversion of 1 of values results in different value.
• the values strings. differ in case. think abc same abc1, sql doesn't.
• you have spaces or other "hidden" characters @ end of string.

and 2 more reasons can think of may not true in databases:

• one value char , other varchar (or wide versions of them). implicit spaces @ end of char make them different.
• one unicode string , other ascii string. 2 characters same not.