SQL IF AND ELSE STATEMENT - sql

Question

I have been trying to execute this if and else statement. However every execution indicates error such as either functional error or syntax related errors.
CREATE trigger [dbo].[TRIAL]
on [dbo].[TBL1]
after INSERT
AS
BEGIN
SET NOCOUNT ON;
IF TBL1.NUMBER = TBL2.NUMBER THEN
insert into TBL3 (NAME,HEIGHT)
select NAME,HEIGHT
from TBL1,TBL2
ELSE
PRINT 'WRONG NUMBER'
end
Would you please be able to help me to correct this?

Answer 1

To expand a bit on Alex K's comment:
declare #Flag bit = 1;
-- ERROR: There is no THEN keyword.
if #Flag = 1 then
select 'A';
-- CORRECT: Omit THEN and this works as expected.
if #Flag = 1
select 'A';
-- ERROR: Only the first SELECT is associated with the IF, so the ELSE is unmatched.
if #Flag = 2
select 'B1';
select 'B2';
else
select 'C';
-- CORRECT: If each branch of the IF has only one statement, then this construction is okay.
if #Flag = 2
select 'B1';
else
select 'C';
-- CORRECT: If you want multiple statements in either branch of the IF, make them into a block using BEGIN/END.
if #Flag = 2
begin
select 'B1';
select 'B2';
end
else
select 'C';
-- CORRECT: You can also use BEGIN/END with single statements if you like.
if #Flag = 2
begin
select 'B1';
select 'B2';
end
else
begin
select 'C';
end