Check constraint to prevent insertion of invalid characters.
A column level check constraint may be used to prevent insertion of data containing characters within a specific ASCII range.
2016-12-12 (first published: 2016-11-30)
2,168 reads
constraints
NULLs to Not NULLs
Script finds char types columns defined to allow NULL values but have non NULL values and generates the ALTER statements for the changes.
2016-02-22 (first published: 2016-02-08)
1,006 reads
Declarative SQL: Using UNIQUE Constraints
In SQL, you can express the logic of what you want to accomplish without spelling out the details of how the database should do it. Nowhere is this more powerful than in constraints. In this introduction to Declarative SQL, Joe Celko demonstrates how you can write portable code that performs well and executes some complex logic, merely by creating unique constraints.
2015-12-15
6,149 reads
2015-11-18 (first published: 2015-10-29)
892 reads
Obedience Training For Databases: Cascading Constraints
In which Phil Factor illustrates in TSQL how it is possible to use foreign key constraints to enforce data rules, and illustrates some surprising consequences of using cascading.
2015-03-30
3,037 reads
Set-based Constraint Violation Reporting in SQL Server
When you're importing data into an RDBMS in bulk and an exception condition is raised because of a constraint violation, you generally need to fix the problem with the data and try again. The error won't tell you which rows are causing the violation. What if you've thousands of rows to search when it happens? There are solutions, writes William Sisson.
2014-10-16
8,821 reads
Handling Constraint Violations and Errors in SQL Server
The database developer can, of course, throw all errors back to the application developer to deal with, but this is neither kind nor necessary. How errors are dealt with is dependent on the application, but the process itself isn't entirely obvious.
2012-07-10
3,666 reads
SQL Server Unique Constraints for Large Text Columns
We are storing large text and URLs that are over 900 bytes in some of our tables and have a requirement to enforce uniqueness in those columns. But SQL Server has a limitation that index size can't be over 900 bytes. How do I enforce uniqueness in these columns and is it possible to achieve this in SQL Server 2005 and above? What are my different options to solve this problem? I heard that we can use CHECKSUM to create a hash, but is it possible to avoid collisions in the hash value as we are storing millions of rows?
2009-11-05
3,006 reads
Should I Use a UNIQUE Constraint or a Unique Index in SQL Server?
I am modifying a table and I need to add a column that must be defined as being unique. I see that SQL Server allows you to define a UNIQUE constraint on a column but I also see that you can create a unique index on a column. Which one should I use?
2008-09-05
8,319 reads
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Question of the Day
The "ORDER BY" clause behavior
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