基于索引值将列从一个表复制到另一个表的 SQL 查询

Question

I am trying to formulate a query that copies the contents of one column in a table to another table and match it up with the index values.

Both tables are going to have the same index values.

Example:

Table1

+-----------------------------------+------------+
|               index               |    val     |
+-----------------------------------+------------+
|                 11                |     AA     |
|                 23                |     AA     |
|                 34                |     BB     |
+-----------------------------------+------------+

Table2

+-----------------------------------+
|               index               |
+-----------------------------------+
|                 34                |
|                 11                |
|                 23                |
+-----------------------------------+

After query is run, make table 2 reflect:

+-----------------------------------+------------+
|               index               |    val     |
+-----------------------------------+------------+
|                 34                |     BB     |
|                 11                |     AA     |
|                 23                |     AA     |
+-----------------------------------+------------+

I would appreciate any help offered. Thanks in advance.

Answer 1

I don't quite understand why you would like to do this, but it could look something like:

Alter table BTABLE add val varchar(10);
update BTABLE  bta set val = (select ata.val from ATABLE ata where ata.index = bta.index);

the only thing is, this way you would have 2 completely identical tables...

Answer 2

The easiest way to do what you describe, is to drop Table2 and recreate it as a copy of Table1 :

DROP TABLE Table2;

CREATE TABLE Table2 AS
SELECT * FROM Table1;

See the demo .
Results (for Table2 ):

> index | val
> ----: | :--
>    11 | AA 
>    23 | AA 
>    34 | BB 

Answer 3

Like Irina Avram told you, Why do you want to copy a column that already exists in your database. You can use JOIN and a SELECT statement to get what you want, without adding more datas in your database.

SELECT Table2.index, Table1.val FROM Table2 JOIN Table1 ON Table2.index = Table1.index

Learn more about JOIN