SELECT IFNULL( c.compId, '1' ) compId, c.compShortName, IFNULL( c.compCompID, '' ) compCompID, IFNULL( c.compName, '未绑定单位' ) compName, COUNT( CASE WHEN checkType = '1' THEN 1 END ) AS jsCount, COUNT( CASE WHEN checkType = '0' THEN 1 END ) AS count, d.compName compCompName FROM checkinfo b LEFT JOIN companyinfo c ON b.checkCompanyId = c.compId LEFT JOIN companyinfo d ON c.compCompId = d.compId WHERE b.STATUS = '1' -- AND c.compName != '未绑定单位' GROUP BY c.compId, checkType ORDER BY count( checkId ) DESC 怎样优化

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1mysql统计数据时sum if、count if、ifnull的使用_count if null ...进一步探索

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2MySQL中IF()、IFNULL()、NULLIF()、ISNULL()函数的使用 ...进一步探索

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3SQL 使用 IFNULL 将空值设为零 - 极客教程进一步探索

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4MySQL IFNULL() 函数 | 菜鸟教程

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5MySQL ifnull()函数 - MySQL教程

yiibai

6SQL的case when then else end语句的用法 - CSDN博客

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7MySQL 中IF/IFNULL/CASE-WHEN-THEN - 简书

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理解问题SELECT IFNULL( c.compId, '1' ) compId, c.compShortName, IFNULL( c.compCompID, '' ) compCompID, IFNULL( c.compName, '未绑定单位' ) compName, COUNT( CASE WHEN checkType = '1' THEN 1 END ) AS jsCount, COUNT( CASE WHEN checkType = '0' THEN 1 END ) AS count, d.compName compCompName FROM checkinfo b LEFT JOIN companyinfo c ON b.checkCompanyId = c.compId LEFT JOIN companyinfo d ON c.compCompId = d.compId WHERE b.STATUS = '1' -- AND c.compName != '未绑定单位' GROUP BY c.compId, checkType ORDER BY count( checkId ) DESC 怎样优化

已完成理解「SELECT IFNULL( c.compId, '1' ) compId, c.compShortName, IFNULL( c.compCompID, '' ) compCompID, IFNULL( c.compName, '未绑定单位' ) compName, COUNT( CASE WHEN checkType = '1' THEN 1 END ) AS jsCount, COUNT( CASE WHEN checkType = '0' THEN 1 END ) AS count, d.compName compCompName FROM checkinfo b LEFT JOIN companyinfo c ON b.checkCompanyId = c.compId LEFT JOIN companyinfo d ON c.compCompId = d.compId WHERE b.STATUS = '1' -- AND c.compName != '未绑定单位' GROUP BY c.compId, checkType ORDER BY count( checkId ) DESC 怎样优化」

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SELECT IFNULL( c.compId, '1' ) compId, c.compShortName, IFNULL( c.compCompID, '' ) compCompID, IFNULL( c.compName, '未绑定单位' ) compName, COUNT( CASE WHEN checkType = '1' THEN 1 END ) AS jsCount, COUNT( CASE WHEN checkType = '0' THEN 1 END ) AS count, d.compName compCompName FROM checkinfo b LEFT JOIN companyinfo c ON b.checkCompanyId = c.compId LEFT JOIN companyinfo d ON c.compCompId = d.compId WHERE b.STATUS = '1' -- AND c.compName != '未绑定单位' GROUP BY c.compId, checkType ORDER BY count( checkId ) DESC 怎样优化

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