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From:Paul DuBois Date:June 13 2002 9:06pm
Subject:Re: Why does Key==Mul in DESCRIBE TABLE for unique key?
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At 3:35 +0800 6/14/02, Andy Sy wrote:
>----- Original Message -----
>From: "Paul DuBois" <paul@stripped>
>To: "Andy Sy" <andy@stripped>; <mysql@stripped>
>Sent: Friday, June 14, 2002 2:45 AM
>Subject: Re: Why does Key==Mul in DESCRIBE TABLE for unique key?
>
>
>>  At 2:03 +0800 6/14/02, Andy Sy wrote:
>>  >mysql> CREATE TABLE X (FLD1 INT UNIQUE);
>>  >Query OK, 0 rows affected (0.05 sec)
>>  >
>>  >mysql> DESCRIBE X;
>>  >+-------+---------+------+-----+---------+-------+
>>  >| Field | Type    | Null | Key | Default | Extra |
>>  >+-------+---------+------+-----+---------+-------+
>>  >| FLD1  | int(11) | YES  | MUL | NULL    |       |
>>  >+-------+---------+------+-----+---------+-------+
>>  >
>>  >Doesn't MUL mean a key can exist multiple times
>>  >in the index?
>>
>>  Right. It means it's part of a non-unique index.
>
>But I declared the field as UNIQUE (see the CREATE
>TABLE statement).

UNIQUE indexes can contain multiple NULL values.

Declare the column as FLD1 INT NOT NULL UNIQUE
and you'll see a difference.

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  • Why does Key==Mul in DESCRIBE TABLE for unique key?Andy Sy13 Jun
    • Re: Why does Key==Mul in DESCRIBE TABLE for unique key?Paul DuBois13 Jun
  • Re: Why does Key==Mul in DESCRIBE TABLE for unique key?Andy Sy13 Jun
    • Re: Why does Key==Mul in DESCRIBE TABLE for unique key?Paul DuBois13 Jun
  • Re: Why does Key==Mul in DESCRIBE TABLE for unique key?Gerald Clark13 Jun
    • Re: Why does Key==Mul in DESCRIBE TABLE for unique key?Paul DuBois13 Jun