SQL

if else sql

IF Boolean_expression
BEGIN
    -- Statement block executes when the Boolean expression is TRUE
END
ELSE
BEGIN
    -- Statement block executes when the Boolean expression is FALSE
END

sql if else

DECLARE 
        a Number := 30;       b Number; 
BEGIN 
        IF a > 40 THEN 
          b := a - 40; 
          DBMS_OUTPUT.PUT_LINE('b=' || b); 
       elseif a = 30 then 
          b := a + 40; 
          DBMS_OUTPUT.PUT_LINE('b=' || b); 
       ELSE 
          b := 0; 
          DBMS_OUTPUT.PUT_LINE('b=' || b); 
       END IF; 
END; 
/

else if sql

UPDATE table 
SET columnB = CASE fieldA 
        WHEN columnA=1 THEN 'x' 
        WHEN columnA=2 THEN 'y' 
        ELSE 'z' 
      END 
WHERE columnC = 1

t-sql if else

IF 1=1
	SELECT 1
ELSE
	SELECT 0
-- returns 1

-- Definition
IF Boolean_expression   
     { sql_statement | statement_block }   
[ ELSE   
     { sql_statement | statement_block } ]