In SQL and relational databases, NULL values are an important part of managing data and information stored in SQL tables. A NULL value is used as a placeholder for missing values or values that are unknown in a database column or cell.
2023-09-11
2023-02-17
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2023-02-06 (first published: 2023-02-03)
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2023-02-06 (first published: 2023-01-23)
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Missing data is a difficult and common problem to solve. In this article, Joe Celko explains several approaches to deleting or replacing missing data.
2018-07-04
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2017-09-11
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2016-09-26
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2016-02-17
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2015-05-01
1,788 reads
It sounds simple enough. Either your column will always have a value or it may not. Yet somehow such a seemingly simple decision can become a never-ending debate where database schema begins to resemble superstition and designing effective tables seems more contentious than you expected it to be.
2016-02-26 (first published: 2014-10-30)
26,514 reads
By Steve Jones
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Let’s consider the following script that can be executed without any error on both SQL Sever and PostgreSQL. We define the table t1 in which we insert three records:
create table t1 (id int primary key, city varchar(50)); insert into t1 values (1, 'Rome'), (2, 'New York'), (3, NULL);If we execute the following query, how will the records be sorted in both environments?
select city from t1 order by city;See possible answers