A database concept used to represent missing, unknown or inapplicable data.

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0
votes
1answer
387 views

H2 SELECT NULLABLE or other equivalent to check a column has NOT NULL constraint or not

I would like to check if a column has a NOT NULL constraint in order to start an automated upgrade of the table definition. However in H2 the SQL SELECT NULLABLE FROM TABLE_NAME doesn't return me the ...
1
vote
2answers
361 views

Expand sparse table with self outer join on distinct values

I have this: g1 | g2 | x ---------+-----------+----- New York | Monday | 210 New York | Tuesday | 258 Chicago | Monday | 30 Chicago | Wednesday | 25 LA | Thursday | 40 ...
0
votes
2answers
146 views

oracle null value in quotes - yet another newbie question

I have a where clause like "and uc.completion_status in ('[P....]') " here ('[P....]') is the user input from taken a dropdown list in the user interface. and dropdown list consists three options ...
2
votes
2answers
2k views

Only one NULL for one part of primary key

I have two date columns : "start date" and "finish date". I want to make sure that there can be only one null value in the "finish date" column (which should be current state if it's NULL) for one ...
3
votes
1answer
737 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
25k 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 ...
3
votes
3answers
2k 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
2k views

Query performance of a NULL vs an empty ('') varchar in SQL Server 2012

I have 3 indexed fields in a query: int, int, and varchar(250). The query performs well when all 3 conditions are specified with real values. The int columns always have values, but there are plenty ...
0
votes
1answer
1k views

Find ID columns with null value in oracle database

I need a way to iterate through all tables in tablespace "T_ECOS" and find all ID with null value in oracle database Any suggestion?
2
votes
1answer
327 views

Null Values and Performance

I always try to build the database avoiding any NULL values in my tables, and I have successfully had done this so far. (Hey, I am very new to database design.) But still there are times when saving ...
18
votes
3answers
3k views

Why does ANSI SQL define SUM(no rows) as NULL?

The ANSI SQL standard defines (chapter 6.5, set function specification) the following behaviour for aggregate functions on empty result sets: COUNT(...) = 0 AVG(...) = NULL MIN(...) = NULL MAX(...) = ...
1
vote
1answer
927 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 ...
12
votes
4answers
1k views

Reason to not use nullable number in Oracle?

Our company is interfacing with another software company for a joint project, and we were told that, if a particular value should not be displayed, we should pass in a -5000 (their arbitrary sentinel ...
2
votes
3answers
11k views

Questions about handling NULLs and empty strings in nvarchar and numeric fields

I understand that questions similar to these pop up often around here. I have searched before posting these but I didn't find any QA threads that completely answer my questions. In a table, I ...
2
votes
2answers
265 views

Proper use of NULL, and utilizing CHECK constraints for business logic vs stored procedures

This question regards the proper use of NULL and utilizing CHECK constraints for business logic vs stored procedures. I have the following tables setup. I normalized the tables to avoid using ...
4
votes
2answers
74 views

Deleting NULL results

Currently I'm just trying to delete objects with the Name column being Null from a temp table with the following... delete from #PulledData where #PulledData.Name0 = NULL I've also tried = 'NULL', ...
2
votes
1answer
3k views

Dealing with NULL values and EMPTY strings in UNION of two tables

I want return records from two database tables when a record differs in at least one of the fields. I have written a query for it using the UNION operator. It is working absolutely fine. However, I ...
4
votes
2answers
187 views

Checking a wide table for nulls [duplicate]

Possible Duplicate: Test if any fields are NULL I am new here. I have a table with 70-odd columns. Is there a way I can check the number of rows with at least one null value in any column ...
4
votes
2answers
5k views

SQL Server 2008R2 - Why is my index not used

I have a table defined in the following way: CREATE TABLE [dbo].[MyTable] ( [MyTable_ID] [int] IDENTITY(1,1) NOT NULL, [COLUMN_WITH_DATA] [varchar](128) NOT NULL, [COLUMN_A] [varchar](128) ...
3
votes
1answer
4k views

Oracle: How to create a not null column in a view

Given a table like: CREATE TABLE "MyTable" ( "MyColumn" NUMBER NOT NULL ); I want to create a view like: CREATE VIEW "MyView" AS SELECT CAST("MyColumn" AS BINARY_DOUBLE) AS "MyColumn" FROM ...
1
vote
2answers
536 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, ...
3
votes
3answers
2k views

Best way to work around NOT IN NULL issue?

There are plenty of explanations of why NOT IN NULL doesn't work, but I didn't see any solutions. (recent question here: Why does NOT IN with a set containing NULL always return FALSE/NULL?) I have 6 ...
12
votes
1answer
2k views

Why does NOT IN with a set containing NULL always return FALSE/NULL?

I had a query (for Postgres and Informix) with a NOT IN clause containing a subquery that in some cases returned NULL values, causing that clause (and the entire query) to fail to return anything. ...
3
votes
1answer
1k 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 ...
7
votes
3answers
3k views

Comparing Columns that can contain NULLS - is there a more elegant way?

I know that you can't compare a value to NULL and expect a result without adding something like in the following code... SELECT * FROM A INNER JOIN B ON A.ID = B.ID WHERE A.STRING ...
3
votes
2answers
484 views

Remove nulls from TSQL connection string

I have a bunch of queries, against a couple different databases, that I use to generate delimited reports. I'm trying to create some new reports against a MSSQL database and I'm having trouble ...
7
votes
1answer
475 views

Adding SPARSE made table much bigger

I have a generic log table, about 5m rows. There's a "strongly typed" field that stores event type, and a bunch of "losely typed" columns that contain data relevant to the event. That is, meaning of ...
7
votes
1answer
8k 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, ...
1
vote
1answer
128 views

Why is replication attempting to distribute NULL values into Identity columns

We are sporadically getting this error: Explicit value must be specified for identity column in our replication environment. I have checked the transaction command that is reporting the error and it ...
5
votes
7answers
784 views

Database table and NULLs

I know that there have been many opinions/sides concerning NULL values in a database. I have not understood though what is the best practice for this. I.e. if I have a relational table with an ...
24
votes
3answers
18k views

PostgreSQL multi-column unique constraint and NULL values

I have a table like the following: create table my_table ( id int8 not null, id_A int8 not null, id_B int8 not null, id_C int8 null, constraint pk_my_table primary key (id), ...
3
votes
4answers
5k views

In SQL Server 2008, how can I get all the columns that are marked as nullable in their schemas even though no records contain NULL for those columns?

In my legacy database, a lot of the time the schema needlessly allows null entries for particular columns. To help find out which columns in particular, I need to do some querying of SQL Server 2008 ...
3
votes
1answer
680 views

PostgreSQL pl/perl trigger, differentiate null vs empty

I've been trying to speed up a generic auditing trigger that I had written in pl/pgsql some time back. On update, it generates a list of columns in the table being updated and inserts rows in the ...
4
votes
1answer
209 views

Is there some drawback to define SPARSE columns?

I have a table which has a lot of NULL values in columns. But some columns don't contain NULLs at all (although nullable). Is there some drawback to declare all of these columns as SPARSE?
6
votes
2answers
3k views

How can I help SQL Server recognize my indexed view column is NOT NULL-able?

I have the following indexed view defined in SQL Server 2008 (you can download a working schema from gist for testing purposes): CREATE VIEW dbo.balances WITH SCHEMABINDING AS SELECT user_id ...
3
votes
0answers
274 views

To NULL or not to NULL? [duplicate]

Possible Duplicate: Why shouldn't we allow NULLs? I've heard that it's a bad idea to do database design such that nullable fields exist. However, eliminating nullables often cause much ...
48
votes
7answers
10k views

Why shouldn't we allow NULLs?

I remember reading this one article about database design and I also remember it said you should have field properties of NOT NULL. I don't remember why this was the case though. All I can seem to ...
9
votes
2answers
1k views

What is the purpose of SET NULL in Delete/Update Foreign Keys constraints?

I am probably being narrow minded, but if I create a foreign key constraint and a row gets updated or deleted, I lose that connection if the child table's column gets set to NULL. What is the purpose ...
12
votes
4answers
759 views

Does NULL have a type?

Various sources (eg Wikipedia, PSOUG) state that Oracle's null does not have a type. Is this true? What about other RDBMSs?
4
votes
4answers
5k views

Why does = NULL not work in Oracle?

I recently realized that we need to use a special syntax IS NULL to compare a literal to NULL. Why does = NULL not work here?
2
votes
1answer
3k 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 ...
1
vote
2answers
1k views

null check and string concatenation

Can I do better than this query? select func_returns_str('key1') || nvl2( func_returns_str('key2'), ',' || func_returns_str('key2'), null) from dual; I ...
3
votes
2answers
2k views

PostgreSQL: count datasets / lines containing NULL values

I'm looking for a easy function to get the number of datasets (of any table) containing NULL values. It's not important how many columns are involved. For example: CREATE TABLE tab1 ( id INTEGER ...
7
votes
4answers
4k views

Finding empty columns of a table in PostgreSQL

What query would return the name of the columns of a table where all rows are NULL?
42
votes
4answers
12k views

What is the difference between select count(*) and select count(any_non_null_column)?

I seem to remember that (on Oracle) there is a difference between uttering select count(*) from any_table and select count(any_non_null_column) from any_table. What are the differences between these ...
0
votes
2answers
701 views

Is where x = 0 or x is null to be replaced by where isnull(x, 0) = 0 resp. where NVL(x, 0) = 0

Think of x as a column containing null, 0, 1. Only less than 1 % of the rows contain 1. There is no logical difference between 0 and Null. Is it a good idea to insist, that isnull rather than NVL is ...
31
votes
2answers
8k 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 ...
53
votes
8answers
16k views

When to use NULL and when to use an empty string?

I'm interested mainly in MySQL and PostgreSQL, but you could answer the following in general: Is there a logical scenario in which it would be useful to distinguish an empty string from NULL? What ...