Subject What is the max varchar column I can index?
Author phil_hhn
Hi, I have Firebird 1.5.3, and need a varchar(250) column in one of my
tables and it needs an index for performance reasons.

1) I created a table which has a varchar(250) column, codeset none,
collation none. I can put an index on this column since it is within
the max size allowed for an index (252 chars, right?).

2) If I recreate the table, specifying the column is codeset
ISO8859-1, collation EN_UK, the largest the column can be (to put an
index on it) is 83 or 84 characters (I also checked this against
Ivans(?) online index size checking tool).

However if I follow step (1) - i.e create the varchar(250) column then
add an index, I can then modify the column to have codeset ISO8859-1,
collation EN_UK, and it seems ok.

So what should be 'legal'? I.e step (2) suggests I should not be
allowed a column of 250 characters (with this codeset/collation) and
have an index on it. And yet I can achieve this by following step (1)
and changing codeset/collation.

What is allowed?