SQL-从2个表中获取数据

Question

I've read other threads about getting queries from 2 tables, but I still don't now how to implement my issue.

There is a Feed page where user gets queries from Table A sorted by date. And there is another Table B that contains some queries. I need to get queries from both tables, mix them, and sort by date.

Table A

----id----  ----date---- ----post----
1           20170514     post 1
2           20170512     post 3
3           20170510     post 5

Table B

----id----  ----date---- ----post---- ----thread----
1           20170513     post 2       1
2           20170511     post 4       2

SELECT * FROM tableA WHERE post!="" AND date!="" and SELECT * FROM tableB WHERE post!="" AND date!=""

Output (in plaint text to screen) should be:

1. table: Table A, post: post 1, date: 20170514
2. table: Table B, post: post 2, date: 20170513
3. table: Table A, post: post 3, date: 20170512
4. table: Table B, post: post 4, date: 20170511
5. table: Table A, post: post 5, date: 20170510

Answer 1

You can use UNION like this

SELECT id, date, post FROM TABLEA
WHERE date IS NOT NULL AND
post IS NOT NULL
UNION
SELECT id, date, post FROM TABLEB
WHERE date IS NOT NULL AND
post IS NOT NULL

you may need to use alias for the tables.

Answer 2

If you'd like to see a result-set containing both tables' rows, you should use JOIN but in this case, you should be able to connect those two tables. For example if you have a product table, and a product_details , then you should have a field on the second table like product_id which is pointing to an existing product's id. you can find out more here:

https://www.w3schools.com/sql/sql_join.asp

Otherwise you could try UNION which is used to combine two ore more result-ser of multiple SELECT statements:

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