tables: make duplicate error in update clearer

[winkyao]

What problem does this PR solve?

Before this pr, we return ERROR 1062 (23000): key already exist when update statement meets duplicate key. In MySQL:

MariaDB [wilan]> create table c(i int,j int,k int,primary key(i,j,k));
Query OK, 0 rows affected (0.00 sec)
 
MariaDB [wilan]> insert into c values(1,2,3);
Query OK, 1 row affected (0.00 sec)
 
MariaDB [wilan]> insert into c values(1,2,4);
Query OK, 1 row affected (0.00 sec)
 
MariaDB [wilan]> update c set i=1,j=2,k=4 where i=1 and j=2 and k=3;
ERROR 1062 (23000): Duplicate entry '1-2-4' for key 'PRIMARY'

ERROR 1062 (23000): Duplicate entry '1-2-4' for key 'PRIMARY' is clearer.

Tests

• Unit test

[jackysp]

Please fix CI @winkyao .

[jackysp]

LGTM

[zimulala]

LGTM

[zimulala]

/run-all-tests

[shenli]

/run-all-tests

[shenli]

Please fix the CI.

[winkyao]

/run-common-test -tidb-test=pr/612

[winkyao]

/run-integration-common-test -tidb-test=pr/612