SQL transaction

What is business
Business ： David and Jonathan
A program execution unit that accesses and may update various data items in a database （unit）, That is, by multiple sql Sentence composition , It must be implemented as a whole A C I D
these sql Statements are submitted to the system as a whole , Or both , Either not ; Transactions are about the possibility of changing table data – Additions and deletions , It's no use to query
Business characteristics ：CUID
1. Atomicity ： Affairs cannot be further divided , Transaction must be atomic unit of work ; For other data modification , Or all , Either not
2. Uniformity ： After transaction , The data needs to be consistent to some extent
3. Isolation, ： Each transaction is independent , Not affected by other transactions
4. persistence ： Once the transaction is committed , Modifications to data are permanently retained
How to use transactions ： Include the add, delete and modify commands you execute between the start and commit of the transaction or the start and rollback .
Grammatical steps ：
Start business ：BEGIN TRANSACTION -- Open transaction
Transaction submission ：COMMIT TRANSACTION -- Submit operation
Transaction rollback ：ROLLBACK TRANSACTION -- Cancel operation
Judge whether there is an error in the execution of a statement ：
Global variables @@ERROR;
@@ERROR You can only judge the current one T-SQL Statement execution error , In order to determine all of the T-SQL Is there an error in the statement , We need to accumulate errors ;
for example ：SET @errorSum = @errorSum + @@ERROR

requirement ：–aa turn 1000 Yuan to bb（cmoney The fields are done check constraint >=1）

declare @cuowuhao int = 0 -- Record the error number that may occur during the execution of the statement 
begin transaction
	update bank set cmoney = cmoney - 1000 where name = 'aa'
	set @cuowuhao = @cuowuhao + @@ERROR -- Just add up an error number 
	update bank set cmoney = cmoney + 1000 where name = 'bb'
	set @cuowuhao += @@ERROR
	select * from bank
	if(@cuowuhao<>0) -- Erroneous , Only after all the statements are executed , Then make an overall judgment 
		rollback transaction
	else
		commit transaction
	select * from bank
go

result ：