MySQL-从数据库中选择所有表

Question

I've a database called test and i've tables called x,y,z.

How do i select x,y,z and there is a column called date IN X,Y,Z check whether there is a particular date.

Is there any build in function that does this?

update

SELECT column date from all tables which is in a database called test

Thanks in advance!!

Answer 1

As far as I know, in SQL you cannot 'select a table', you can select some column(s) from one or many tables at once. The result of such a query is an another table (temporary table) that you retrieve the data from.

Please be more specific about what exactly you want to do (eg: "I want to select a column 'z' from table 'tableA' and column 'y' from table 'tableB'") - then I'm sure your question has a pretty simple answer :)

SELECT x.date AS x_date, y.date AS y_date, z.date AS z_date FROM x,y,z;

That produces a result:

+---------+---------+---------+
| x_date  | y_date  | z_date  |
+---------+---------+---------+
|         |         |         |
|         |         |         |
+---------+---------+---------+

Alternatively you can get everything in one column by ussuing a query:

SELECT date FROM x
UNION ALL
SELECT date FROM y
UNION ALL
SELECT date FROM z;

That produces a result:

+-------+
| date  |
+-------+
|       |
|       |
+-------+

In the example above you would get also duplicate values in the single column. If you want to avoid duplicates replace 'UNION ALL' with 'UNION' I'm still not sure if I undestood what you really want ot achieve, but I still hope that helps

Also take a look at:

http://www.w3schools.com/sql/sql_union.asp

http://www.sql-tutorial.net/SQL-JOIN.asp