如何将ifnull与窗口函数一起使用？
比方说我在下面有这个查询结果，lag1只是使用window函数向下移动的预算列，因此，该值为null。但是我想用零替换该null，以便我可以计算预算和lag1之间的差。
select id, budget,
lag(budget) over (order by id) as lag1
from projects;
+----+---------+---------+
| id | budget | lag1 |
+----+---------+---------+
| 1 | 1000000 | NULL |
| 2 | 100000 | 1000000 |
| 3 | 100 | 100000 |
+----+---------+---------+
我尝试了以下两个示例，但不起作用：
select id, budget,
ifnull(lag(budget),0) over (order by id) as lag1
from projects;
select id, budget,
ifnull((lag(budget) over (order by id) as lag1),0)
from projects;
答案 0 :(得分：1)
lag()最多接受三个参数。第一个是返回值的表达式。这只是列名。第二个参数决定了它应该落后多少行。默认值为1。第三，对您来说有趣的是，如果未找到上一行，则为默认值。
因此，您可以直接在lag()调用中定义默认值：
SELECT id,
budget,
lag(budget, 1, 0) OVER (ORDER BY id) lag1
FROM projects;
答案 1 :(得分：0)
我猜您的import React, { Component } from 'react';
import { Row, Col } from 'antd';
import PageHeader from '../../components/utility/pageHeader';
import Box from '../../components/utility/box';
import LayoutWrapper from '../../components/utility/layoutWrapper.js';
import ContentHolder from '../../components/utility/contentHolder';
import basicStyle from '../../settings/basicStyle';
import IntlMessages from '../../components/utility/intlMessages';
import { adalApiFetch } from '../../adalConfig';
const data = {
TenantId: this.state.tenantid,
TenanrUrl: this.state.tenanturl,
TenantPassword: this.state.tenantpassword
};
const options = {
method: 'post',
data: data,
config: {
headers: {
'Content-Type': 'multipart/form-data'
}
}
};
export default class extends Component {
constructor(props) {
super(props);
this.state = {TenantId: '',TenanrUrl:'',TenantPassword:''};
this.handleChangeTenantUrl = this.handleChangeTenantUrl.bind(this);
this.handleChangeTenantPassword = this.handleChangeTenantPassword.bind(this);
this.handleChangeTenantId= this.handleChangeTenantId.bind(this);
this.handleSubmit = this.handleSubmit.bind(this);
}
handleChangeTenantUrl(event){
this.setState({tenanturl: event.target.value});
}
handleChangeTenantPassword(event){
this.setState({tenantpassword: event.target.value});
}
handleChangeTenantId(event){
this.setState({tenantid: event.target.value});
}
handleSubmit(event){
alert('A name was submitted: ' + this.state.value);
event.preventDefault();
this.data.append("TenantId", this.state.tenantid);
this.data.append("TenanrUrl", this.state.tenanturl);
this.data.append("TenantPassword", this.state.tenantpassword);
const options = {
method: 'post',
data: this.data,
config: {
headers: {
'Content-Type': 'multipart/form-data'
}
}
};
adalApiFetch(options)
.then(response => response.json())
.then(responseJson => {
if (!this.isCancelled) {
this.setState({ data: responseJson });
}
})
.catch(error => {
console.error(error);
});
}
upload(e){
let data = new FormData();
//Append files to form data
let files = e.target.files;
for (let i = 0; i < files.length; i++) {
data.append('files', files[i], files[i].name);
}
}
render(){
const { data } = this.state;
const { rowStyle, colStyle, gutter } = basicStyle;
return (
<div>
<LayoutWrapper>
<PageHeader>{<IntlMessages id="pageTitles.TenantAdministration" />}</PageHeader>
<Row style={rowStyle} gutter={gutter} justify="start">
<Col md={12} sm={12} xs={24} style={colStyle}>
<Box
title={<IntlMessages id="pageTitles.TenantAdministration" />}
subtitle={<IntlMessages id="pageTitles.TenantAdministration" />}
>
<ContentHolder>
<form onSubmit={this.handleSubmit}>
<label>
TenantId:
<input type="text" value={this.state.tenantid} onChange={this.handleChangeTenantId} />
</label>
<label>
TenantUrl:
<input type="text" value={this.state.tenanturl} onChange={this.handleChangeTenantUrl} />
</label>
<label>
TenantPassword:
<input type="text" value={this.state.tenantpassword} onChange={this.handleChangeTenantPassword} />
</label>
<label>
Certificate:
<input onChange = { e => this.upload(e) } type = "file" id = "files" ref = { file => this.fileUpload } />
</label>
<input type="submit" value="Submit" />
</form>
</ContentHolder>
</Box>
</Col>
</Row>
</LayoutWrapper>
</div>
);
}
}
版本低于8.0，因为您的第二个解决方案已经完成。
mysql如果您的select id, budget, ifnull(lag(budget) over (order by id),0) as lag1
from projects;
版本低于8.0，则需要在mysql中编写一个子查询，以在select前获得行数据
TESTDDL
ID查询
CREATE TABLE projects(
ID INT,
budget INT
);
INSERT INTO projects VALUES (1,1000000);
INSERT INTO projects VALUES (2,100000);
INSERT INTO projects VALUES (3,100);
[结果] ：
SELECT *,IFNULL((select budget FROM projects t1 WHERE t.id > t1.id order by t1.id desc limit 1 ) ,0) lag1
FROM projects t