select distinct on two tables

[mfyahya]

I have two tables, both containing an 'authors' column. Is there a way
to get a unique list of authors from the two tables?
I tried SELECT DISTINCT `authors` from `table1`, `table2`;
but I got an "Column 'authors' in field list is ambiguous" error.

Is there also a query to return only the count of distinct authors from
the two tables?

Thanks for any help.

[Bill Karwin]

mf*****@gmail.com wrote:

I have two tables, both containing an 'authors' column. Is there a way
to get a unique list of authors from the two tables?
I tried SELECT DISTINCT `authors` from `table1`, `table2`;
but I got an "Column 'authors' in field list is ambiguous" error.
Try this:
(SELECT `authors` FROM `table1`)
UNION
(SELECT `authors` FROM `table2`)
ORDER BY `authors`

See http://dev.mysql.com/doc/mysql/en/union.html for more information.
Is there also a query to return only the count of distinct authors from
the two tables?

For aggregates over multiple tables, I think you'd have to start using
MERGE tables, but this can be used only if the tables have identical
columns.
http://dev.mysql.com/doc/mysql/en/me...ge-engine.html

Another method would be to use a TEMPORARY table:
CREATE TEMPORARY TABLE authorlist (`authors` VARCHAR(100));
INSERT INTO authorlist SELECT DISTINCT `authors` FROM `table1`;
INSERT INTO authorlist SELECT DISTINCT `authors` FROM `table2`;
SELECT DISTINCT `authors` FROM `authorlist`;
SELECT COUNT(DISTINCT `authors`) FROM `authorlist`;

Regards,
Bill K.

[mfyahya]

Thanks very much !