Tagged Questions

0
votes
1answer
49 views

Creating a partial unique constraint for MySQL

I have the same question as asked in a previous post: PostgreSQL multi-column unique constraint and NULL values. But the solution there is not applicable as I am using MySQL instead of PostgreSQL. My ...
0
votes
1answer
53 views

WITH ROLLUP WHERE NULL = x

I tried to find this question somewhere else on here, and found a couple that were similar to it -- but all the answers seemed pretty convoluted, and I think it was surprising to me because I just ...
3
votes
1answer
126 views

A function to check if a column allows NULL

Is there a way to write an insert/update query that checks if a column allows NULLs: If it does set the column to NULL, and '' (empty string) otherwise? I would be something like: UPDATE mytable ...
3
votes
2answers
2k views

Select column names whose entries are not null

I would like to have a list of those columns of a table that have at least one not-NULL data entries in them. In other words, I would like to get the column names for which the following returns at ...
2
votes
3answers
182 views

Empty LONGTEXT or NULL?

In my MySQL DB I have one field called html_contents that contains all the html to be shown in a webpage. Obviously the html could be huge, and certaintly bigger than 64KB, therefore I decided to use ...
1
vote
1answer
342 views

How to change the display of an empty string in mysql command line tool?

I'm maintaining a database with InnoDB tables. These tables have some columns of type (from show create table): `val0` varchar(30) default NULL, `val1` varchar(30) default NULL, etc... From the ...
1
vote
2answers
128 views

MYSQL only Show columns which allow null

I need to be able to pull the column names which allow a NULL value, I know that show columns from TABLE Will give show me the table properties and whether or not the column allows null values, ...
2
votes
1answer
414 views

Are many NULL columns harmful in mysql InnoDB?

As I explored the clustered B-tree index system of InnoDB, I think that the presence of many NULL (or small) columns has no significant effect on InnoDB performance. Does the presence of excess ...
4
votes
1answer
3k views

MySQL column defined with NOT NULL is allowing nulls

I had created a table a while back and started adding data to it. Recently I added a new column (address) to it with NOT NULL as part of the new column. The old rows (pre-addition) are still null, ...
2
votes
1answer
1k views

MySQL - LOAD DATA INFILE - Handling unescaped NULL in INFILE or creating INFILE with escaped NULL

I am selecting data from a database on server A, dumping the output into a file locally, and then doing a LOAD DATA INFILE on my local database. The bash command looks something like this: mysql -e ...
26
votes
2answers
4k views

NULL or NOT NULL by default?

In MySQL, is it better to always allow nulls unless you know a field is required, or always use Not Null unless you know a field will contain nulls? Or doesn't it matter? I know in some DBMSs they ...