MySQL唯一约束> 16列

Question

I want to use normalization as much as I can. However, just can't wrap my head around this one.

Suppose I have financial data as such:

ledger# | dimension1 | dimension2 | dimension3

4000 | 100 | 200 | 300

5113 | 100 | 298 | 300

I need to be sure that every combination of these 4 columns is unique. I know about the unique constraint, so I put a 'unique' on all the mentioned columns.

But...what if the number of dimension columns has to be 25, so there will be 25 dimension columns instead of the 3 mentioned? How would I go around as to use a unique constraint? I know a constraint can hold only hold 16 columns or 3072 bytes, no more.

I was thinking of using a hash of some sort, but haven't quite figured out how to do that.

can anyone help me by providing an idea / info / example?

If there is a totally different idea of accomplishing this without a unique constraint, I'm all for hearing about it!

Answer 1

Option1:

CREATE TABLE bigboy (
  ledger_sub1 int unsigned not null COMMENT 'foreign key me...',
  ledger_sub2 int unsigned not null COMMENT 'forgein key me...'
  PRIMARY KEY (ledger_sub1,ledger_sub2)
)

CREATE TABLE bigboy_sub1 {
 ledger int unsigned auto_increment,
 dim01 int unsigned not null,
 ...
 dim15 int unsigned not null,
 PRIMARY KEY (ledger),
 UNIQUE KEY uk1 (dim01..dim15)
)

CREATE TABLE bigboy_sub2 {
 ledger int unsigned auto_increment,
 dim16 int unsigned not null,
 ...
 dim30 int unsigned not null,
 PRIMARY KEY (ledger),
 UNIQUE KEY uk1 (dim16..dim30)
)

ledger_sub1 = INSERT IGNORE INTO bigboy_sub1(dim01..dim15) and return ledger;
ledger_sub2 = INSERT IGNORE INTO bigboy_sub2(dim16..dim30) and return ledger;
its_unique = INSERT IGNORE INTO bigboy(ledger_sub1,ledger_sub2);

Option2:

CREATE TABLE bigboy {
 ledger int unsigned auto_increment,
 dim01 int unsigned not null,
 ...
 dim30 int unsigned not null,
 bigboy_uniq VARCHAR(301) not null,
 PRIMARY KEY (ledger),
 UNIQUE KEY uk1 (bigboy_uniq)
);
where bigboy_uniq = concatenation of LPAD'ed dim01..dim30

Option3:

CREATE TABLE bigboy {
 ledger int unsigned auto_increment,
 dim01 int unsigned not null,
 ...
 dim30 int unsigned not null,
 fingers_crossed VARCHAR(32) not null,
 PRIMARY KEY (ledger),
 UNIQUE KEY uk1 (fingers_crossed)
);
where fingers_crossed = md5 of LPAD'ed dim01..dim30 string

(disclaimer - i wouldn't use any these alone unless hacking around)