ifnull(count(id),0)
时间: 2023-11-28 21:47:58 浏览: 31
这是一个 SQL 语句中常用的函数,用于统计某个字段的非空值数量。它的作用是,如果 id 字段不为空,则返回 id 的数量;否则返回 0。在某些情况下,这种函数可以用于替代 IF 或 CASE 语句,以便更简洁地实现某些逻辑。例如,在查询某张表的记录数量时,可以使用如下语句:
```
SELECT ifnull(count(id), 0) FROM table_name;
```
这将返回表 table_name 中 id 字段非空值的数量,如果该字段全为空,则返回 0。
相关问题
SELECT IFNULL( count( nt.id ), 0 ) total, IFNULL( count( ta.id ), 0 ) endtotal, cs.taskname,nt.id,nt.name FROM nk_xjsg_taskresult nt JOIN nk_xjsg_constask cs ON cs.id = nt.taskid AND cs.customerid = nt.customerid AND cs.pid = '40289e8c87fff7f80188042c15d50010' JOIN nk_xjsg_consplan nc ON nc.id = cs.pid AND nc.customerid = cs.customerid LEFT JOIN ( SELECT id, resultid, statusnum, statusname, endnum FROM nk_xjsg_taskresult_date WHERE customerid = '40289e8c8803a391018803a6ef8f0000' ) ta ON ta.resultid = nt.id and ta.statusnum = '40' -- AND ta.number = 1 -- -- AND ta.endnum = nt.resultnum WHERE nt.customerid = '40289e8c8803a391018803a6ef8f0000' GROUP BY cs.taskname ,nt.id ,nt.name; 为什么第一个total是5 不应该是1吗 怎么修改成1
根据你提供的SQL查询语句,第一个total是通过COUNT函数统计的nt.id的数量,因此结果为5。如果你想让第一个total只统计一次nt.id的数量,可以将COUNT函数的参数改为DISTINCT,即将“COUNT(nt.id)”改为“COUNT(DISTINCT nt.id)”。这样就可以确保只统计nt.id的不同值,从而得到正确的结果。修改后的SQL查询语句如下:
SELECT IFNULL(COUNT(DISTINCT nt.id), 0) total, IFNULL(COUNT(ta.id), 0) endtotal, cs.taskname, nt.id, nt.name
FROM nk_xjsg_taskresult nt
JOIN nk_xjsg_constask cs ON cs.id = nt.taskid AND cs.customerid = nt.customerid AND cs.pid = '40289e8c87fff7f80188042c15d50010'
JOIN nk_xjsg_consplan nc ON nc.id = cs.pid AND nc.customerid = cs.customerid
LEFT JOIN (
SELECT id, resultid, statusnum, statusname, endnum
FROM nk_xjsg_taskresult_date
WHERE customerid = '40289e8c8803a391018803a6ef8f0000'
) ta ON ta.resultid = nt.id and ta.statusnum = '40' -- AND ta.number = 1 -- AND ta.endnum = nt.resultnum
WHERE nt.customerid = '40289e8c8803a391018803a6ef8f0000'
GROUP BY cs.taskname, nt.id, nt.name;
SELECT IFNULL(COUNT(DISTINCT nt.id), 0) total, IFNULL(COUNT( DISTINCT ta.id), 0) endtotal, cs.taskname, nt.id, nt.name FROM nk_xjsg_taskresult nt JOIN nk_xjsg_constask cs ON cs.id = nt.taskid AND cs.customerid = nt.customerid AND cs.pid = '40289e8c87fff7f80188042c15d50010' JOIN nk_xjsg_consplan nc ON nc.id = cs.pid AND nc.customerid = cs.customerid LEFT JOIN ( SELECT id, resultid, statusnum, statusname, endnum FROM nk_xjsg_taskresult_date WHERE customerid = '40289e8c8803a391018803a6ef8f0000' ) ta ON ta.resultid = nt.id and ta.statusnum = '40' -- AND ta.number = 1 -- AND ta.endnum = nt.resultnum WHERE nt.customerid = '40289e8c8803a391018803a6ef8f0000' GROUP BY cs.taskname, nt.id, nt.name; 怎么让endtotal的值从5变成1
根据你提供的SQL查询语句,endtotal的值是通过COUNT函数统计的DISTINCT ta.id的数量,因此结果为5。如果你想让endtotal的值从5变成1,需要在COUNT函数中加入条件,只统计符合要求的数据。根据你的需求,可以在COUNT函数的参数中加入条件“ta.endnum = nt.resultnum”,确保只统计符合要求的数据。修改后的SQL查询语句如下:
```
SELECT IFNULL(COUNT(DISTINCT nt.id), 0) total, IFNULL(COUNT(DISTINCT CASE WHEN ta.endnum = nt.resultnum THEN ta.id ELSE NULL END), 0) endtotal, cs.taskname, nt.id, nt.name
FROM nk_xjsg_taskresult nt
JOIN nk_xjsg_constask cs ON cs.id = nt.taskid AND cs.customerid = nt.customerid AND cs.pid = '40289e8c87fff7f80188042c15d50010'
JOIN nk_xjsg_consplan nc ON nc.id = cs.pid AND nc.customerid = cs.customerid
LEFT JOIN (
SELECT id, resultid, statusnum, statusname, endnum
FROM nk_xjsg_taskresult_date
WHERE customerid = '40289e8c8803a391018803a6ef8f0000'
) ta ON ta.resultid = nt.id and ta.statusnum = '40' -- AND ta.number = 1
WHERE nt.customerid = '40289e8c8803a391018803a6ef8f0000'
GROUP BY cs.taskname, nt.id, nt.name;
```
修改后的查询语句中,将第二个COUNT函数的参数改为“DISTINCT CASE WHEN ta.endnum = nt.resultnum THEN ta.id ELSE NULL END”,这样只有符合条件的数据才会被统计。