MySQL in its standard configuration has this wonderful "feature" of truncating your data if it can't fit in the field.

mysql> create table foo (bar varchar(4));
Query OK, 0 rows affected (0.00 sec)

mysql> insert into foo (bar) values ("12345");
Query OK, 1 row affected, 1 warning (0.00 sec)

In comparison, PostgeSQL does:

psql=> create table foo (bar varchar(4));
CREATE TABLE
psql=> insert into foo (bar) values ('12345');
ERROR:  value too long for type character varying(4)

You can make MySQL do the right thing by setting the SQL Mode option to include STRICT_TRANS_TABLES or STRICT_ALL_TABLES. The difference is that the former will only enable it for transactional data storage engines. As much as I'm loathed to say it, I don't recommend using STRICT_ALL_TABLES, as an error during updating a non-transational table will result in a partial update, which is probably worse than a truncated field. Setting the mode to TRADITIONAL includes both these and a couple of related issues (NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_DIVISION_BY_ZERO) You can set the mode using:

• On the command line:

  --sql-mode="TRADITIONAL"

• In /etc/mysql/my.cnf:

  sql-mode="TRADITIONAL"

• At runtime:

  SET GLOBAL sql_mode="TRADITIONAL"
  SET SESSION sql_mode="TRADITIONAL"

Just say no to databases that happily throw away your data