SQL表联接问题

Question

I have two tables, Table 1 and 2. I want to update information at Table 1 based on Table 2. For example, correct AA in table 1 from 10 to 30.

What quires should I write?

Thanks,

Answer 1

you don't want to do a join from what I can tell, but instead you should do an update. It does get a bit more complicated when you're using data from another table instead of feeding raw data straight into the query.

UPDATE Table1 t1,
     Table2 t2
SET t1.num = t2.num
WHERE t1.name == t2.name;

not the exact code of course because the question and tables are somewhat vague but I believe this is the right direction.

Answer 2

Try an update with a join.

UPDATE TABLE1 a JOIN TABLE2 b ON a.join_colA = b.join_colA
SET a.numberColumn = b.numberColumn

Here column join_colA is your first column numberColumn would be your other value column.

Answer 3

I would solve this problem in 3 steps

Step 1: Join the tables
Step 2: Update the null values from table 1
Step 3: Drop the unnecessary column

Select A.*, B.Column2 as column3 from A
left join B
on A.Column1=B.Column1


update table1
set column3= column2

alter table table1
drop column column2

Figure out the syntax errors that you may encounter