mysql三目运算实现if, else的效果，避免不必要的查询

if(expr1, expr2, expr3) 如果expr1为真,返回expr2，则否返回expr3

case when then else end 结构

CASE case_value
    WHEN when_value THEN statement_list
    [WHEN] when_value THEN statement_list] ...
    [ELSE statement_list]
END CASE

Or:

CASE 
    WHEN search_condition THEN statement_list
    [WHEN search_condition] THEN statement_list] ...
    [ELSE statement_list]
END CASE

case 1 when 1 then "b" else " c" end

case when ifnull(name, '')='' then 0 else 1 end