如何使用mysql连接具有相同属性但每个表中数据不同的2个表

Question

Table 1

create table itemType1(
  maincatg varchar(25), 
  subcatg varchar(25), 
  price float(5), 
  primary key(maincatg, subcatg) 
);

Table2

create table itemType2(
     maincatg varchar(25), 
     subcatg varchar(25), 
     price float(5), 
     primary key(maincatg, subcatg) 
);

Answer 1

It sounds like you're looking for a UNION rather than a JOIN .

(SELECT maincatg, subcatg, price
FROM itemType1)

UNION ALL

(SELECT maincatg, subcatg, price
FROM itemType2)

This is effectively a concatenation of the two tables.

Beyond that, I'm really not sure what you're hoping to accomplish.

Answer 2

This kind of table is going to be much easier to work with.

create table item(
  maincatg varchar(25),
  subcatg varchar(25), 
  price float(5),
  type tinyint(1),
  primary key(maincatg, subcatg) 
);

It also looks like you're going to have a lot of duplicate data in your maincatg and subcatg columns. If I was doing it I would have those in another table or possibly two. You join them with ids.

You will probably have an easier time if you read up on database normalization. It's an easy concept to brush up on as long as you find a decent tutorial and there are plenty out there.

If you're stuck using a database that you can't change for whatever reason, you should probably edit your question to say so, or else most answers will probably be similar to mine.