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

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4
votes
4answers
297 views

How to exclude NULL values inside CONCAT MySQL?

If I have this - tadd is the Address table: CONCAT(tadd.street_number, ' ', tadd.street_name,', ', tadd.apt_number,', ', tadd.city,', ', ...
2
votes
1answer
30 views

Unique Index/Constraint with multiple columns, one column is nullable

My questions is whether it's possible to have unique index comprised of multiple columns where one of the columns may contain NULL. Example: A table named 'regulated_person' has a number of columns ...
3
votes
1answer
69 views

Display non-null and null count using case statement

In total there are 10 values in my table, 5 of which are null. I need to display the count using case statement in Oracle, like output below: Sample Data: +------+ | Eid | +------+ | 1 | | 2 ...
2
votes
1answer
58 views

Why does coalescing make this query quicker?

I have the following query SELECT SQL_NO_CACHE `table1`.* FROM `table1` LEFT JOIN `table2` ON table2.id = table1.table2_id WHERE (`table2`.`date_assigned` >= '2015-06-21') AND ( ...
1
vote
1answer
67 views

Null in Varchar datatype

I am using a SQL Server database. If NULL value is inserted to a VARCHAR datatype column, what will be the memory size used for the column?
58
votes
8answers
5k views

Does SQL Server read all of a COALESCE function even if the first argument is not NULL?

I'm using a T-SQL COALESCE function where the first argument will not be null on about 95% of the times it is ran. If the first argument is NULL, the second argument is quite a lengthy process: ...
4
votes
3answers
5k views

Test if any fields are NULL

I'm trying to figure out an easy query I can do to test if a large table has a list of entries that has at least ONE blank (NULL / empty) value in ANY column. I need something like SELECT * FROM ...
14
votes
5answers
8k views

Why does a UNIQUE constraint allow only one NULL?

Technically, NULL = NULL is False, by that logic no NULL is equal to any NULL and all NULLs are distinct. Shouldnt this imply that all NULLs are unique and a unique index should allow any number of ...
3
votes
1answer
116 views

VARCHAR NULL storage

I read somewhere online and in a Microsoft Press book there is a field declaration attribute that can be used to indicate NULL VARCHAR values should not consume space at the leaf-level instead of ...
1
vote
1answer
21 views

Normalize End Date - Nulls or separate table

I was hoping for some advice on best practice in schema design - as far as End Date values are concerned. In this case it is for a Suppliers table - we are required to store information on the Start ...
2
votes
0answers
39 views

Better performance to have nullable columns or an extra table? [duplicate]

There are many ways to get rid of nulls in tables, and I have heard of various reasons to get rid of them, but can anyone show me some real numbers as to how your database might perform differently ...
0
votes
1answer
413 views

MySQL is inserting “” as 0 in decimal fields. How to stop that?

The fields are nullable, so they do allow nulls. Why would MySQL convert "" to 0 instead of NULL? Is there a way to force it to be NULL instead?
1
vote
1answer
41 views

Strange behaviour in TSQL function (parameter with int variable or NULL behaves differently)?

I experienced very strange problem today with TSQL function. The function has several parameters (int and bit). One of the (int) is set with value NULL. When calling a function with NULL inside the ...
1
vote
0answers
23 views

How to best distinguish between “types” of missing data?

I am working on large tables (> 100 fields each) currently organized in flat-files in csv-format. An Oracle DB is to be created to store all the data and allow for several more or less intricate ...
1
vote
1answer
225 views

LEFT JOIN DEFAULT NULL VALUE

My query can be simplified as this: SELECT a.id, a.name, b.* FROM a LEFT JOIN b ON a.id=b.id Which b is from group concat select (very dynamic column). Sometimes there are 3 columns in b, sometimes ...
0
votes
2answers
32 views

How to get the second string in the ORA-02296 error to show something meaningful

Whenever I run the following script*: ALTER TABLE ANIMAL.MONKEY MODIFY TAIL_COUNT NOT NULL; I receive the following error: ORA-02296: cannot enable (ANIMAL.) - null values found I have a ...
5
votes
1answer
142 views

MySQL loading NULLs in numeric columns

MySQL 5.6.23, InnoDB I am loading tables from character delimited text files using the LOAD DATA INFILE commnd and I would like every field with a \N, which is the NULL character in this setting, to ...
1
vote
1answer
29 views

always error “cannot insert value NULL” sqlserver

I want to update table "tmpiscunitmap.tr_kpi_id" year_period=2016 with value from table "tmp_kpi.tr_kpi_id where year_period=2016" with condition tmpiscunitmap.tr_kpi_id = tmp_kpi.tr_kpi_id on ...
1
vote
1answer
39 views

generate new column from another table column, treating nulls are unique

I have a table that looks like the following: |device_id | login_id | ----------------------- | 1 | NULL | | 2 | A | | 3 | A | | 4 ...
3
votes
3answers
76 views

Is it better to create another table to possible null values in relational databases?

I'm designing a relational database to use in MySQL. I have the next situation: In one table there are fields that in the most of situations are NULL. The fields would be like: Table name: tabla ...
0
votes
1answer
22 views

How to prevent #Error values derived from Nulls in an outer join

Suppose I have two tables to outer join Tab1: ID Nam 1 Joe 2 Moe 3 Flo Tab2: ID Val y w 1 stuff 66 33 2 duff 67 44 and one of the resulting columns is derived -- i.e., ...
1
vote
0answers
20 views

Null Dimensions in SSAS [closed]

Several years ago 2008, I create a data warehouse using Business Objects. Business Objects did not process Outer Joins well and used SQL for all of its queries. Therefore, for every dimension I ...
0
votes
2answers
579 views

mysql UNIQUE KEY multiple columns with one column as NULL

I understand the way UNIQUE KEY works in Mysql 5.5+, and understand that NULL allows duplicate entries to be created. In following schema and I would finally want that family_relation should have ...
3
votes
0answers
282 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 ...
0
votes
0answers
30 views

Postgresql indexing for IS NULL

I have two similar queries, whose only difference (in the last two lines) is that one uses IS NULL while the other compares defined values. Query #1 takes only a few minutes: UPDATE ...
0
votes
1answer
56 views

Filling not applicable fields with N/A rather than leaving them empty or Null [duplicate]

I have a database of few million records, many of the fields (call them Ec1 to EcN) have either Null or empty string in them. When I looked at them more closely, I found that for many records, several ...
1
vote
2answers
114 views

How to select data in the same table on different rows that are empty?

I use this select on my SQLite database: SELECT attributeX FROM table GROUP BY attributeX HAVING COUNT(attributeY) = 0; My table: attributeX (type integer) | attributeY (type text) ...
0
votes
3answers
971 views

Two nullable columns one required to have value

No-Explanation Question: Is there anyway to have a constrain of 2 null values that always requires 1 to have value ? For example two date columns both null but having at least 1 that requires to have ...
0
votes
1answer
130 views

SQL Server's aggregate functions ignore nulls. How do I correct this?

According to MS's knowledgebase, Except for COUNT, aggregate functions ignore null values. Does anyone know how I can get it to work correctly, that is, return a null if it attempts to ...
56
votes
8answers
21k 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 ...
34
votes
3answers
25k 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), ...
2
votes
1answer
79 views

Efficient manual cleanup of foreign keys in MySQL [closed]

I have an all-InnoDB database in MySQL (Percona) 5.6 that was previously using FK constraints. I had to give up on them as I kept running into locking issues, so I removed the constraints and added ...
1
vote
1answer
46 views

Pivoting with NULL Dates

I'm attempting the pivot below: SELECT EmpID as ID, [1] as January, [2] as February, [3] as March, [4] as April, [5] as May, [6] as June, [7] ...
0
votes
2answers
396 views

insert inserted id to another table

Here's the scenario: create table a ( id serial primary key, val text ); create table b ( id serial primary key, a_id integer references a(id) ); create rule a_inserted as on insert to a do ...
61
votes
7answers
13k 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 ...
3
votes
3answers
26k views

Getting SELECT to return a constant value even if zero rows match

Consider this select statement: SELECT *, 1 AS query_id FROM players WHERE username='foobar'; It returns the column query_id with value 1 along with a player's other columns. How would ...
8
votes
3answers
4k 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 ...
1
vote
0answers
91 views

How to replace empty, multi-column result with single 'none'

If it is possible to make query in Oracle which will return single column/row with value "none" instead of empty, multi-column result? Otherwise return proper amount of columns with result. This is ...
4
votes
4answers
7k 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?
0
votes
1answer
38 views

multi-column FKs with NULL values

I understand that in PostgreSQL if there is a multi-column FK from table B to table A and one or more of the FK columns in table B are nullable then the FK is still considered as "honored" for the ...
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 ...
0
votes
1answer
34 views

Dealing with co-dependent not null columns

Say I have a table entities (subclassed by people and organizations tables), where each entry requires a primary_email_id. The entities table looks like this: entities ======== id INT AUTO_INCREMENT ...
2
votes
1answer
609 views

How to index a query `WHERE field IS NULL` (postgres)

So I basically have a table with lots of inserts, setting one of the fields (uploaded_at) to NULL. Then a periodic task selects all the tuples WHERE uploaded_at IS NULL, processes them and updates, ...
1
vote
1answer
422 views

Populate one table with data from another one on selected cells

I have a problem with filling empty cells in one table with data from another one. I got a table with user emails - some of the fields are empty, some are already containing emails. I gathered the ...
0
votes
1answer
87 views

If I assign a NVL constraint to a nullable column will it display an error or it will retrieve the records?

I have a database in which some tables have to be joined to fetch the data. The problem is that in one table the column is nullable (nullable is set to yes or no constraint given for that column) and ...
1
vote
1answer
87 views

What relevance does the table-level ANSI_NULL setting have?

Apparently, SQL Server stores the current ANSI_NULL setting when creating a table (see related questions here and here). However, when I execute SELECT * FROM myVeryOldTable WHERE ...
0
votes
0answers
386 views

Oracle 12c, exclude rows wher two columns are both null

Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit I am trying to select rows with a non-null value in one of two columns. Data is being selected from a view (MY_VIEW) with both ...
2
votes
2answers
3k views

How do I include nulls during comparisons in SQL Server?

So basically in SQL Server a NULL means there is no value and thus can't be compared which returns some unexpected results. For example, the following query doesn't return rows where value IS NULL ...
1
vote
0answers
23 views

How do I include nulls during comparisons in SQLServer? [duplicate]

So basically in SQLServer a NULL means there is no value and thus can't be compared which returns some unexpected results. For example, the following query doesn't return rows where value IS NULL but ...
1
vote
3answers
6k views

Select query to retrieve values even if are null

I need some help in a query. Need to retrieve data from 1 table, even if one of the field has null value. Here's an example: Select name, SUM(credit) as credit From expenses Where name like ...