mysql select column default value if is null
SELECT
`w`.`city` AS `city`,
`w`.`city_en` AS `city_en`,
`w`.`date_y` AS `date_y`,
`w`.`week` AS `week`,
`w`.`cityid` AS `cityid`,
`w`.`temp1` AS `temp1`,
`w`.`temp2` AS `temp2`,
`w`.`temp3` AS `temp3`,
`w`.`temp4` AS `temp4`,
`w`.`temp5` AS `temp5`,
`w`.`temp6` AS `temp6`,
`w`.`weather1` AS `weather1`,
`w`.`weather2` AS `weather2`,
`w`.`weather3` AS `weather3`,
`w`.`weather4` AS `weather4`,
`w`.`weather5` AS `weather5`,
`w`.`weather6` AS `weather6`,
`w`.`wind1` AS `wind1`,
`w`.`wind2` AS `wind2`,
`w`.`wind3` AS `wind3`,
`w`.`wind4` AS `wind4`,
`w`.`wind5` AS `wind5`,
`w`.`wind6` AS `wind6`,
`w`.`fl1` AS `fl1`,
`w`.`fl2` AS `fl2`,
`w`.`fl3` AS `fl3`,
`w`.`fl4` AS `fl4`,
`w`.`fl5` AS `fl5`,
`w`.`fl6` AS `fl6`,
`w`.`ind` AS `ind`,
`w`.`index_xs` AS `index_xs`,
`w`.`index_uv` AS `index_uv`,
`w`.`index_xc` AS `index_xc`,
`w`.`index_tr` AS `index_tr`,
`w`.`index_co` AS `index_co`,
`w`.`index_cl` AS `index_cl`,
`w`.`index_ls` AS `index_ls`,
`w`.`index_ag` AS `index_ag`,
`w`.`create_time` AS `create_time`,
`sk`.`temp` AS `temp`,
`sk`.`wd` AS `wd`,
`sk`.`ws` AS `ws`,
`sk`.`sd` AS `sd`,
`sk`.`wse` AS `wse`,
`sk`.`time` AS `time`,
`sk`.`create_time` AS `create_time_sk`,
COALESCE(`air`.`aqi`,0) AS `aqi`,
COALESCE(`air`.`level`,'') AS `level`,
COALESCE(`air`.`position_name`,'') AS `position_name`
FROM (SELECT * FROM `ep_weather_report_current` WHERE `city`='汝州') w
LEFT JOIN `ep_weather_sk_temperature_current` `sk` ON `w`.`cityid` = `sk`.`cityid`
LEFT JOIN (SELECT * FROM `ep_airpollution_realtime_current` WHERE `city` = `position_name` AND city = '汝州') `air`
ON `w`.`cityid` = `air`.`cityid`
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COALESCE(`air`.`aqi`,0) AS `aqi`,
COALESCE(`air`.`level`,'') AS `level`,
COALESCE(`air`.`position_name`,'') AS `position_name`
