如何在sql中用0消除NULL

Question

我现在有一个简单的表，当我运行 sql 语句时，它应该使用 mysql 将 NULL 替换为 0

这是我迄今为止尝试过的

SELECT IFNULL(targetbuttonname, 0), sessions.sid, events.datetime, count(*) as num_rows,
  count(distinct sessions.sid) as sessions, 
  sum( targetbuttonname = 'kredyt' ) as num_kredyt, 
  sum(devicetype ='Computer') as num_computer from events 

现在当我运行我的脚本时，它仍然返回 null

这里是演示demo

我的查询语句有什么问题？

Answer 1

使用COALESCE

SELECT coalesce(NULL,0), sessions.sid, events.datetime, count(*) as num_rows, count(distinct sessions.sid) as sessions, 
  sum( targetbuttonname = 'kredyt' ) as num_kredyt, 
  sum( targetbuttonname = 'konto' ) as num_konto,
  sum( targetbuttonname = 'czat' ) as num_czat,
  sum( targetbuttonname = 'video-voice_btns' ) as num_voice,
  sum( targetbuttonname = 'video-close_btn' )  as num_close,
  sum( targetbuttonname = 'video-muted_btn' ) as num_muted,
  sum( targetbuttonname = 'video-play_btn' )  as num_play,
  sum( targetbuttonname = 'video-pause_btn' )  as num_pause,
  sum( targetbuttonname = 'video-replay_btn' ) as num_replay, 
  sum(watchtime) as num_watchtime, 
  sum(devicetype ='Computer') as num_computer from events  INNER JOIN sessions ON (events.sid =sessions.sid) WHERE events.datetime BETWEEN '2019-11-11' AND '2019-11-21'

演示：http://sqlfiddle.com/#!9/3cf3cf/10

IFNULL 也可以使用：

SELECT ifnull(targetbuttonname,0), sessions.sid, events.datetime, count(*) as num_rows, count(distinct sessions.sid) as sessions, 
  sum( targetbuttonname = 'kredyt' ) as num_kredyt, 
  sum( targetbuttonname = 'konto' ) as num_konto,
  sum( targetbuttonname = 'czat' ) as num_czat,
  sum( targetbuttonname = 'video-voice_btns' ) as num_voice,
  sum( targetbuttonname = 'video-close_btn' )  as num_close,
  sum( targetbuttonname = 'video-muted_btn' ) as num_muted,
  sum( targetbuttonname = 'video-play_btn' )  as num_play,
  sum( targetbuttonname = 'video-pause_btn' )  as num_pause,
  sum( targetbuttonname = 'video-replay_btn' ) as num_replay, 
  sum(watchtime) as num_watchtime, 
  sum(devicetype ='Computer') as num_computer from events  INNER JOIN sessions ON (events.sid =sessions.sid) WHERE events.datetime BETWEEN '2019-11-11' AND '2019-11-21'

这里是演示：http://sqlfiddle.com/#!9/3cf3cf/14