How to select unique records by SQL - Stack Overflow
How to select unique records by SQL Asked 16 years, 4 months ago Modified 2 years, 1 month ago Viewed 751k times
sql - Difference between Select Unique and Select Distinct - Stack …
Dec 3, 2008 · Unique was the old syntax while Distinct is the new syntax,which is now the Standard sql. Unique creates a constraint that all values to be inserted must be different from the others.
sql - What is the difference between a primary key and a unique ...
32 A primary key is a unique field on a table but it is special in the sense that the table considers that row as its key. This means that other tables can use this field to create foreign key relationships to …
How can I create a SQL unique constraint based on 2 columns?
Jul 5, 2011 · The users are importing data from various external systems so ContactId will not be unique across the board but will be unique on a per user basis. I know how to create Unique and Non-Null …
sql - How to select only the first rows for each unique value of a ...
In the table, one customer like John Smith can have multiple addresses. I need the SELECT query for this table to return only first row found where there are duplicates in 'CName'. For this table it should …
sql - Diferença na utilização Indice Unique e Unique Constraint no ...
Como referência do que pode ser tão diferente e que estou interessado em saber, segue abaixo um link de como é em um banco Informix , mas no MySQL como funciona? Link, situação similar em outro …
sql - Counting unique records across two tables - Stack Overflow
Jul 24, 2025 · I have two tables The first table is my INVOICEHEADER which contains one record per invoice, but multiple records per order. InvoiceNumber is the unique key on this table (there is no …
sql - unique in where clause - Stack Overflow
Mar 11, 2020 · Please pass in where clause where unique (select distinct teaches.id from teaches where instructor.id = teaches.id and year = 2009 );
sql - Unique vs Distinct keyword in Oracle - Stack Overflow
Oct 6, 2008 · 1 UNIQUE is used for defining contraints on the data that can be stored in the table. DISTINCT is used in queries to remove duplicates from the result set, without affecting the …
sql server - Unique constraint on multiple columns - Stack Overflow
Aug 13, 2010 · If the table is already created in the database, then you can add a unique constraint later on by using this SQL query: