Mssqlsql efficiently associates with the update batch update of subqueries

Mssqlsql efficiently associates with the update batch update of subqueries

Mssql SQL efficiently associates with the update batch update of subqueries

Mssql SQL efficiently associates with the update batch update of subqueries
/*
Update with associated subqueries
-- 1. Create a test table

Create TABLE Table1
(
A varchar (10 ),
B varchar (10 ),
C varchar (10 ),
CONSTRAINT [PK_Table1] PRIMARY KEY CLUSTERED
(
A ASC
)
) ON [PRIMARY]

Create TABLE Table2
(
A varchar (10 ),
C varchar (10 ),
CONSTRAINT [PK_Table2] PRIMARY KEY CLUSTERED
(
A ASC
)
) ON [PRIMARY]
GO
-- 2. Create Test Data
Insert into Table1 values ('zhao ', 'asds', null)
Insert into Table1 values ('money', 'asds ', '123 ')
Insert into Table1 values ('sun', 'asds ', '80 ')
Insert into Table1 values ('lil', 'asds ', null)

Insert into Table2 values ('zhao ', '90 ')
Insert into Table2 values ('money', '123 ')
Insert into Table2 values ('sun', '80 ')
Insert into Table2 values ('lil', '95 ')
GO
Select * from Table1

-- 3. Update through Update
Update Table1 set c = (select c from Table2 where a = Table1.a) where c is null
GO

-- 4. display the updated result
Select * from Table1
GO
-- 5. Delete the test table
Drop TABLE Table1
Drop TABLE Table2