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MDEV-10142 - bb-10.2-compatibility / MDEV-10574


Hello Alexander,
Sometime ago, when I ask you about plan for MDEV-10574, you replied :

>The current plan is to do these transformations:
>1. Transform Insert
>- insert values ("") -> insert values (null)
>2. Transform Select
>- where v=x => (v <> "" and V=X)
>- where v is null => (v="" or v is null)
>We didn't plan to change functions yet. Thanks for bringing this up.
>We'll discuss this.

I've done some tests just by changing :
- insert an Item_null instead of an Item_string when $1.length==0 in rule text_literal of sql_yacc_ora.yy
- return null instead of an empty string in Item_str_func::make_empty_result

My first tests seem promising.

Of course this solution does not allow to "see" the records created with empty strings as null values.
I don't see the importance of being able to do this in a transparent way.
We can explicitly select these row by adding rtrim on these columns.

If you are interesting, I can begin to write a test to evaluate the coverage of this solution.

Best regard.

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