Join/Update between Three Tables - mysql

Question

Currently to get data updated in Table3 that depends on conditions in Tables1 and Table2 I am doing this:
Update Table_B as T1
Inner Join Table_A as T2
On T1.S_ID=T2.ID
Set T1.Percent = T2.Percent
Update Table_C as T1
Inner Join Table_B as T2
On T1.ID=T2.J_ID
Set T1.B = T2.B
Where T2.Percent=100
I would like to not store or update TableB with TableA Percent and somehow do the join in a single statement.

Answer 1

update table_b T1 set T1.Percent=(select T2.Percent from table_a T2 where T1.S_ID=T2.ID)
update table_c T1 set T1.B=(select T2.B from table_b T2 where T1.ID=T2.J_ID) where exists(select * from table_b T3 where T1.ID=T3.J_ID and T3.percent=100)

Answer 2

This isn't valid syntax in an UPDATE statement
Set T1.Percent as T1.Percent
^^
And this isn't valid
Set T1.B as T2.B
^^
The syntax in the UPDATE statements in the question do not look valid.
The SET assignment operator is an equals sign, not an As keyword.
And T1.Percent = T1.Percent doesn't make much sense, since there doesn't seem to be any point to setting a column to its current value.
It's not clear what it is you are actually trying to achieve, without some example data, and the desired end result.
To write a multi-table UPDATE statement, I first write a SELECT statement that returns the primary (or unique) keys of the tables that I am going to update, along with the current values of the columns to be updated, and expressions that return the new values that are going to be assigned to the columns
Based on the SQL in the question, it looks like you might want two joins, something like this:
SELECT ...
FROM table_a a
JOIN table_b b
ON b.s_id = a.id
JOIN table_c c
ON c.id = b.j_id
WHERE a.percent = 100
ORDER BY ...
(We don't know anything about the cardinality of the columns and relationships, whether those are one-to-one, one-to-many, zero-or-one-to-one, etc. We're just guessing.)
To evaluate and test the query, I'd include the primary keys of the tables. I'm going to guess id is the primary key of (the unfortunately named) Table_A and Table_C. And guess that the tuple (j_id,s_id) is a UNIQUE KEY in Table_B.
I will also include the column to be updated (to show the current value), and an expression that returns the new value to be assigned to the column.
Something like this:
SELECT a.id AS `a__id`
, a.percent AS `a__percent`
, b.j_id AS `b__j_id`
, b.s_id AS `b__s_id`
, c.id AS `c__id`
, c.b AS `c__b_old`
, b.b AS `c__b_new`
FROM table_a a
JOIN table_b b
ON b.s_id = a.id
JOIN table_c c
ON c.id = b.j_id
WHERE a.percent = 100
ORDER
BY c.id
, a.id
I would test that, and make sure it's returning the rows from Table_C that I want to update, and that the value returned for the c__b_new expression is the value that I want to assign to the b column in Table_C.
Once I get the SELECT statement working correctly (and only after I get it working correctly), I convert that to a multitable UPDATE.
Just replace the SELECT ... FROM part with the keyword UPDATE.
And before the WHERE clause, add a SET clause that does the assignment of the new value to the column. (I use the same expression I used in the SELECT list to return the new value.)
UPDATE table_a a
JOIN table_b b
ON b.s_id = a.id
JOIN table_c c
ON c.id = b.j_id
SET c.b = b.b
WHERE a.percent = 100
That's just an example of how I go about writing a multi-table UPDATE. There is no guarantee that this statement is going to work for what you need. Again, it's not clear what you are trying to achieve; the specification is too vague; so we're only guessing.