使用SQL IN子句获取给定年级的学生分数，例如阅读中的1,2,3,4。学生可能不会收到任何分数为4的分数。有没有办法选择IN SQL子句中不匹配的条件
这是查询
select
score,
count(*) as [countTimes]
from ScoresTable
where score IN (1,2,3,4)
得分
如果学生从未收到过4，则需要创建一个行，例如4,0 结果集示例
Score Count
1 2
2 3
3 1
4 0
当前查询正在使用IN子句。如果没有与IN子句匹配的记录，则该行不会被disislayed
Score Count
1 2
2 3
3 1
4 0
答案 0 :(得分：2)
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]
class SearchItem extends React.Component {
render() {
return (
<div className="container">
<div className="image-container">
<img className="cover" src={`https://image.tmdb.org/t/p/w500/${this.props.image}`} />
</div>
<div className="info-container">
<p className="title">{this.props.title}</p>
<p>Genre: {this.props.genre}</p>
</div>
</div>
)
}
}
class List extends React.Component {
state = {
selectedStreamUrl: "",
searchInput: "",
showDeleteButton: false,
searchByGenre: false,
list: listData,
filteredList: listData,
filterBy: 'title',
}
//search
startSearch = (value) => {
const search = value.toLowerCase();
const searchKey = this.state.filterBy;
this.setState({
searchInput: value,
filteredList: this.state.list.filter(item => {
return item && item[searchKey].toLowerCase().includes(search)
}),
showDeleteButton: value ? true : false,
})
}
setAllLists = (allLists) => {
console.log("setAllLists")
console.log(this.state.searchByGenre)
this.setState({ filteredList: allLists })
//document.body.style.backgroundColor = "red";
}
removeInput = () => {
this.setState({
filterBy: 'title',
showDeleteButton: false,
searchInput: '',
}, () => this.startSearch(this.state.searchInput));
}
filterBy = (event) => {
const filter = event.target.value;
this.setState({
filterBy: filter
});
}
render() {
return (
<div class={style.list_container}>
<div>
<input value={this.state.searchInput} class={style.searchBar} type="text" id="searchField" placeholder={this.state.searchInput} onChange={(e) => this.startSearch(e.target.value)} ></input>
<select onChange={this.filterBy}>
<option selected={this.state.filterBy === 'title'} value="title">Title</option>
<option selected={this.state.filterBy === 'genre'} value="genre">Genre</option>
</select>
</div>
{
this.state.filterBy === 'genre' ?
<h1>ja</h1>
:
<h1>nee</h1>
}
{
this.state.showDeleteButton ?
<button class={style.deleteButton} onClick={() => this.removeInput()}>Remove</button>
: null
}
{
this.state.filteredList.map((item, index) => {
return <SearchItem image={item.poster_path} title={item.title} genre={item.genre} />
})
}
</div>
);
}
}
ReactDOM.render(<List />, document.getElementById('root'));
</script>：
left join答案 1 :(得分：1)
如果您没有一个具有可用分数值的表，只需“构建”一个表，然后重做这样的查询（在@Serg注释后更新）
select
S.score,
count(ST.Score) as [countTimes]
from
( Select 1 as Score
union all
Select 2 as Score
union all
Select 3 as Score
union all
Select 4 as Score ) as S
left join
ScoresTable ST on S.Score = ST.Score
GROUP BY
S.score
ORDER BY
S.score
答案 2 :(得分：0)
左加入得分列表和ScoresTable
select
sl.score,
count(st.score) as [countTimes]
from (
values (1),(2),(3),(4)
) sl (score)
left join ScoresTable st on st.score = sl.score
group by sl.score