在MySQL上创建表时的两个主键

Question

I'm new to MySql! I'm trying to create a table with 2 primary key or what is usually called a composite key.

CREATE TABLE MovedProduct
(
   MigrationId nvarchar(150)   NOT NULL,
   ContextKey nvarchar(300)  NOT NULL,
   Model varbinary(65535) NOT NULL,
   ProductVersion nvarchar(32) NOT NULL,
   primary key(MigrationId,ContextKey)
)

but I'm getting an error that I can't figure out.

Error Code: 1071. Specified key was too long; max key length is 1000 bytes

I don't what to decrease the keys size because they can get up to their respective size.

Is there something special I need to do in order to have my table created?

Answer 1

You should reduce you field length for the involved fields .. because some charset don't use only one byte for a char but more so .. when these fileds will stored could exeed the limit for keys length

eg :

CREATE TABLE MovedProduct
(
   MigrationId nvarchar(64)   NOT NULL,
   ContextKey nvarchar(128)  NOT NULL,
   Model varbinary(65535) NOT NULL,
   ProductVersion nvarchar(32) NOT NULL,
   primary key(MigrationId,ContextKey)
)

you your charset use 3 bytes for store a char then in your sample you have 3*150 + 3*400 = 1650
instead 3*64 + 3*128 = 576

Answer 2

If you don't need utf8, then explicitly specify latin`:

MigrationId varchar(150)  CHARACTER SET latin1  NOT NULL,
ContextKey  varchar(300)  CHARACTER SET latin1  NOT NULL,