To supplement the basic knowledge, part of the summary of commonly used process control statements

1 -- BEGIN... END: Execute multiple TSQL statements together

BEGIN TRANSACTION 
SELECT @@TRANCOUNT--Transaction counting,Result 1
IF @@TRANCOUNT=0
	BEGIN--Statement block start
		SELECT TOP 1 * FROM dbo.LthUinfo
		ROLLBACK TRAN
		PRINT 'ROLLBACK1'
	END--Statement Block End
ROLLBACK TRAN--Roll back transactions, count minus 1
SELECT @@TRANCOUNT--Here result 0
PRINT 'ROLLBACK2'
--Result: Print message ROLLBACK2

2--IF..ELSE:IF the Boolean expression after IF is true execution, it executes its statement, and it executes the post-ELSE statement for false execution.

IF DATENAME(WEEKDAY,CURRENT_TIMESTAMP) IN('Sunday','Saturday')
	PRINT 'Today is the weekend'
ELSE
	PRINT 'Today is a working day.';
--Be careful if..else in ELSE Is an optional keyword,Usually they execute the first statement next to it
--If more than one can be used BEGIN..END Formal Implementation of Containing Statement Blocks

3--WHILE: Loop statement that repeats execution as long as the condition specified for the loop is true
- Several keywords commonly used in control loops: BREAK,CONTINUE

DECLARE @count AS INT=0
WHILE @count<10
	BEGIN
		IF @count=4
			BEGIN
				SET @count+=1
				CONTINUE--Break this cycle, ignore it CONTINUE The following statement continues

//Start the next cycle
			END

		PRINT 'count='+CAST(@count AS CHAR);
		SET @count+=1

		IF @count=6
			BREAK;--End the current loop. If it's an internal nested loop, it ends the inner loop and starts

//External circulation
	END
--Output results:
/*
count=0                             
count=1                             
count=2                             
count=3                             
count=5  */

4--GOTO: Jump the execution flow to the tag to execute the statement after the tag

--CASE It's a scalar expression.,Can't be used to control execution flow
--GOTO It must be followed by a label and cannot be replaced by a variable.
DECLARE @label AS INT=1
DECLARE @value AS VARCHAR(20)
/*
CASE WHEN @label=1 THEN GOTO ONE
	 WHEN @label=2 THEN GOTO TWO
	 WHEN @label=3 THEN GOTO THREE
	END
	*/
SET @value=CHOOSE(@label,'ONE','TWO','THREE')--according to label Value returns the following index value
SELECT @value--Returns the result: ONE
IF @value='ONE' GOTO ONE --
IF @value='TWO'	GOTO TWO
IF @value='THREE' GOTO THREE
--Define labels
ONE:
	PRINT 'ONE'
	GOTO OVERV
TWO:
	PRINT 'TWO'
THREE:
	PRINT 'THREE'
OVERV:
	PRINT 'over'
PRINT 'Output test'
--Returns the result:
ONE
over
//Output test

--Note: If GOTO If the statement points to the tag, it is the starting point for processing, and all the following statements can be executed
--Whether used or not GOTO Statements and labels can be used as annotation methods.

5--RETURN: Execution is immediate and complete and can be used to exit from a process, batch, or statement block at any time. RETURN
The following statement is not executed. Usually used for stored procedures or functions to return a value.

DECLARE @count AS INT=0
DECLARE @count2 AS INT=10
WHILE @count2>0
BEGIN
WHILE @count<10
	BEGIN
		IF @count=4
			BEGIN
				SET @count+=1
				CONTINUE--Break this cycle, ignore it CONTINUE The following statement continues

//Start the next cycle
			END

		PRINT 'count='+CAST(@count AS CHAR);
		SET @count+=1

		IF @count=6
			--BREAK;--End this cycle
			RETURN;--End the batch statement and execute the stream so far that none of the following statements will persist

//That's ok
	END
	PRINT 'ok'
	SET @count2-=1
END
GO
--Be careful, RETURN Statements are used to end batch statements, execute the stream to this end, everything OVER Now. here RETURN Default return

//Back to 0, but you can't get it and use it.
--usually RETURN Returns a value for a function or stored procedure

6--WAITFOR prevents execution of batches, stored procedures, or transactions until a specified time or interval has passed

SELECT GETDATE();
WAITFOR
	--DELAY '00:00:05.001'--Fixed time interval, maximum not more than 24 hours
	TIME '16:18'--Fixed time point, 16:18 p.m.
	SELECT GETDATE();

7 - throw, try.. Catch to be continued