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hding is right. In that case, declare a multicolumn unique index. That does precisely what you are asking for. MySQL will look at the first column first, so it should be the more unique. [OB] A table needs a primary key.

create table depends (uses varchar(80) not null, usedby varchar(80) not null, unique deps (usedby,uses)); # naming the index is unnecessary, but may be a convenience

Btw, why not represent a leaf node by usedby=NULL? That would give a faster select for leaf/branch.

After Compline,
Zaxo


In reply to (Unique Index) Re x 3: How to count rows using DBI & mysql - Performance results by Zaxo
in thread How to count rows using DBI & mysql - Performance results by Brovnik

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