How to improve update query performance

Question

Why update query takes too much time?

table1

Id      table2Id(Unique key)    
101        201
102        205

table2

Id    table1Id Name bool
201      101  'A'    0
202      101  'B'    0
203      101  'C'    0
205      102  'A'    0
206      102  'B'    0

Table 1 will contain only one table2 Id(one to one). But table2 contain multiple table1 id(one(table2) to many(table1))

update table 2 set bool=1
where Id( select t2.Id from table2 join table1 on t2.Id(PKey)=t1.table2Id(PKey) and t2.Name='A')

This query takes time to update around 6mins. If I run inner select query within 2sec getting results.

If I change join on condition like t1.Id=t2.table1Id then update query executes within 5sec.

Any idea why?

Answer 1

This is your query which works well for you. However, this is not valid SQL update query in terms of any other DBMS Product.

update table 2 set 
where Id( select t2.Id from table2 join table1 on t2.Id(PKey)=t1.table2Id(PKey))

So, let me correct you with SQL update quert with above

UPDATE t1 SET table2Id = t2.Id -- Whaterver going to update
FROM table1 t1 
INNER JOIN table2 t2 
ON t2.Id = t1.Id -- whatever input parameter you have for logical/physical join operation 

Now, in terms of performance the above is perform well if table1(Id) has primary key constraint or index.