Read the comment too, How not to optimize a MySQL query

Read Debunking GROUP BY myths

SELECT ContactID, LastName, FirstName
   FROM Contacts
   WHERE (LastName, FirstName) IN
   (SELECT LastName, FirstName
       FROM Contacts
       WHERE Active = 1
       GROUP BY LastName, FirstName
       HAVING COUNT(*) > 1)
   ORDER BY LastName, FirstName

Source Finding and Eliminating Duplicate Data

Along a similar line, but less complicated, I wanted a list of all unique email addresses, along with some additional fields, so SELECT DISTINCT EmailAddress would not suffice. Here’s the solution I’m using:

SELECT EmailAddress, ContactID, FirstName, LastName
FROM Contacts
WHERE SubscribeNewsletter = 1
GROUP BY EmailAddress
ORDER BY LastName ASC, FirstName ASC

I was a little unsure about the above code, as my references seemed to indicate that GROUP BY needed to work with an aggregate clause, so I reverse-engineered it (read, ran some opposite queries), and am confident the one above is accurate.

I’m open to critique.

UPDATE

It should be noted that the second query above, “works” in as much as you get only one row with one name and email address. You do not get all of the names associated with that particular address. In my case, this is what I wanted, all email addreses just once, along with a name, any name that uses that address is fine.

Additionally, this query worked just fine in MySQL, but didn’t work in PostGresSQL. Thanks to my great friend Rudy, he pointed me in the right direction with the following.

SELECT EmailAddress
       , max(ContactID) as max_ContactID
       , max(FirstName) as max_FirstName
       , max(LastName)  as max_LastName
  FROM Contacts
  WHERE SubscribeNewsletter = 1
  GROUP BY EmailAddress
  ORDER BY max_LastName ASC, max_FirstName ASC

Some resources for further reading …

• Employees with the same first and last names in SQL
• Common SQL questions – Duplicates
• Debunking GROUP BY myths

update [table_name] set [field_name] = replace([field_name],'[string_to_find]','[string_to_replace]');

Source

Comparison is an integral part of most SELECT queries, and MySQL comes with numerous functions for this; at last count, it had over 20 such operators and functions, ranging from well-known ones like = and LIKE to more esoteric ones like NOT IN and STRCMP(). (Article dated: February 9, 2007)

Read: Get more data comparison options in MySQL with operators you may not know

Read the Article…

Read SQL COPY TABLE Command

Here’s what I used, in case I need it again.

CREATE TABLE VolunteerInfo
SELECT ContactID,
	WhyVolunteer,
	Availability,
	AddNotes,
	VTaskID,
	VolunteerWith,
	OtherTask,
	DateCreated,
	CreatedByID,
	DateModified,
	ModifiedByID
FROM Contacts
WHERE WhyVolunteer <> ''
	or Availability <> ''
	or AddNotes <> ''
	or VTaskID <> ''
	or VolunteerWith <> ''

228 records created, add an auto-increment Primary Key for my new table, and humming along to something else.

Note: To make an existing field an auto-increment Primary Key, you must first make the field a Primary Key, then make it an Auto Increment. Must be done in two steps.

Get the adovbs file