MSSQL SQL Efficient Correlated subquery Update batch Update

/* Update--1 using an update with the associated subquery . Create a test table

Create TABLE Table1 ( a varchar (ten), B varchar (ten), C varchar (ten), CONSTRAINT [pk_ Table1] PRIMARY KEY CLUSTERED ( a ASC ) ) on [PRIMARY]

 create TABLE table2     (     a varchar (ten),      C varchar (ten),      CONSTRAINT [pk_table2] PRIMARY KEY Clustered     (     a ASC < Span class= "Apple-converted-space" >   )     ) on [ Primary]     go     

< Span class= "Apple-converted-space" >< Span class= "Apple-converted-space" >< Span class= "Apple-converted-space" >--2. Creating test Data     

< Span class= "Apple-converted-space" >< Span class= "Apple-converted-space" >< Span class= "Apple-converted-space" >insert into Table1 values (' Zhao ', ' ASDs ', null)     

< Span class= "Apple-converted-space" >< Span class= "Apple-converted-space" >< Span class= "Apple-converted-space" > Insert into Table1 values (' money ', ' ASDs ', ' + ')     

< Span class= "Apple-converted-space" >< Span class= "Apple-converted-space" >< Span class= "Apple-converted-space" >< Span class= "Apple-converted-space" >insert into Table1 values (' Sun ', ' ASDs ', ' ')      

Insert into Table1 values (' Lee ', ' ASDs ', null)

Insert into Table2 values (' Zhao ', ' all ')

Insert into Table2 values (' money ', ' + ')

Insert into Table2 values (' sun ', ' + ')

Insert into Table2 values (' Li ', ' up ')

GO SELECT * from Table1

--3. Updating with update mode

Update Table1 Set c = (select C from Table2 where a = table1.a) where c is null GO

--4. Displaying the updated results

SELECT * FROM Table1

GO

--5. Deleting a test table

Drop TABLE Table1

Drop TABLE Table2

MSSQL SQL Efficient Correlated subquery Update batch Update