It sounds like you may be attempting to insert the string 'NULL'
into the char(1)
field, rather than an SQL NULL, and you have strict SQL mode enabled, which prevents this being truncated to N
.
If you are able, run
SHOW CREATE TABLE <your_table_name>
in the MySQL shell to determine whether your target field accepts NULLs. With no context (are you running this as pure SQL, or connecting to the database from some client program in another langauge?) it's difficult to provide the exact solution, but you may have something like this:
INSERT <your_table_name>
SELECT first_name, 'NULL', last_name
where 'NULL' is simply a string with no special meaning, when what you intend is
INSERT <your_table_name>
SELECT first_name, NULL, last_name
Here's an illustration:
mysql> CREATE TABLE my_table ( middle_initial CHAR(1) NULL );
mysql> INSERT INTO my_table SELECT 'NULL';
mysql> SHOW WARNINGS;
Level Code Message
Warning 1265 Data truncated for column 'middle_initial' at row 1
mysql> SELECT * FROM my_table;
middle_initial
--------------
N
mysql> set sql_mode = 'STRICT_TRANS_TABLES';
mysql> INSERT INTO my_table SELECT 'NULL';
ERROR 1406 (22001) at line 16: Data too long for column 'middle_initial' at row 1
mysql> INSERT INTO my_table SELECT NULL;
mysql> SELECT * FROM my_table;
middle_initial
--------------
N
NULL
Bit of a punt - apologies if no use ...