找出列是否在mysqli中支持“ Null”值

Question

I have a mysql database of 100's of tables. Some columns allow null value, some don't. I am inserting data into the table dynamically in php mysqli. I am using the following code to insert any null values:

$value = ($value == "") ? null : $value;

But, the problem with this is I am getting Column 'XXX' cannot be null error. How can I determine if the column supports Null values?

Please help.

Answer 1

You can get all information you need about database structure through the database information_schema , like this one (you want the column IS_NULLABLE ):

SELECT COLUMN_NAME, DATA_TYPE, IS_NULLABLE, COLUMN_DEFAULT
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'tbl_name'
  AND table_schema = 'db_name'
  AND column_name = 'col_name'

Reference: http://dev.mysql.com/doc/refman/5.0/en/columns-table.html

Answer 2

In your database set the DEFAULT value "" (empty string) for fields wich IS NOT NULL. So if you insert NULL value the MySQL will substitute it with default "".

OR

SHOW COLUMNS FOR `table_name`;

Look at field named Null

Answer 3

You can get this info from information_schema database ( IS_NULLABLE field)-

SELECT
  TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, IS_NULLABLE
FROM
  information_schema.COLUMNS
WHERE
  TABLE_SCHEMA = 'db_name' AND TABLE_NAME = 'table_name'; -- specify your filter

Answer 4

You can run the following query:

SHOW COLUMNS FROM `table_name_here`

Which will give you something like the following output:

Field  Type              Null  Key  Default  Extra
id     int(10) unsigned  NO    PRI  NULL     auto_increment
name   varchar(200)      YES        NULL

If you have access to the table information_schema , you can do:

SELECT IS_NULLABLE
FROM   COLUMNS
WHERE  TABLE_NAME   = "table name"
AND    TABLE_SCHEMA = "db_name"
AND    COLUMN_NAME  = "column name"
LIMIT  1

(I've edited the following query to add the TABLE_SCHEMA column from Doug's accepted answer, in case anyone finds this answer later)

Answer 5

I wouldn't blindly translate an empty string to mysql NULL at all.
That's actually 2 different values, each have it's distinct features - so, swapping them may lead to unpredictable results.

The same goes for the trading PHP's NOLL into Mysql' NULL. They may have different meaning too.