Control structures syntax; IF THEN ELSE, CASE, WHILE .

IF THEN ELSE

The IF THEN ELSE syntax in TSQL is kinda weird if you ask me … I forget them ‘all the time’, created examples below for my reference.

IF THEN

if 1 = 1
begin 
  print 'true'
end
 
go
 

IF THEN – short notation

if 1 = 1
  print 'true'
 
go
 

IF THEN ELSE

if 1 = 1
begin
  print 'true'
end
 
else  

begin
  print 'false'
end
 
go
 

IF THEN ELSE – short notation

if 1 = 1
  print 'true'
else  
  print 'false'

go
 

Multiple IF THEN ELSE blocks

if 1 = 1
begin
  print '1 = 1'
end
else  
if 1 = 2
  begin
    print '1 = 2'
  end
else
if 1 = 3
begin
  print '1 = 3'
end
 
go
 

CASE

TSQL has the CASE control structure …

declare @i int, @r int
 
set @i = 1
 
set @r = 
  case @i
    when 1 then 1
    when 2 then 2
      else 0
  end
 
print @r
 
go
 

WHILE

Eternal loop

while 1 = 1 
  print 'true'
 
go
 

Simple WHILE loop

declare @i int
set @i = 0
 
while @i < 10
begin
  print @i
  set @i = @i + 1
end
 
go