if else query in mysql

问题

i need an example of nested if-else condition in mysql query

回答1:

You could also use case statements for if-else conditions

SELECT
  (CASE field1
    WHEN 'A' THEN 'value is A'
    WHEN 'B' THEN 'value is B'
    ELSE 'value is neither A or B'
  END)
FROM your_table;

or

SELECT
  (CASE
    WHEN (field1 IS NULL) THEN 'value is NULL'
    WHEN (field1 = 1) THEN 'value is 1'
    ELSE 'value is neither NULL or 1'
  END)
FROM your_table;

回答2:

You mean the IF(expr, expr, expr) function as defined here? An example would be:

SELECT
  name, ID,
  IF(category = 'fulltime', 1, 
    IF(category = 'parttime', loading, 0)) AS equivloading
FROM
  person

来源：https://stackoverflow.com/questions/3059136/if-else-query-in-mysql