我有一张表table1，如下所示
+----+------+------+------+------+------+
| id | loc | val1 | val2 | val3 | val4 |
+----+------+------+------+------+------+
| 1 | loc1 | 10 | 190 | null | 20 |
| 2 | loc2 | 20 | null | 10 | 10 |
+----+------+------+------+------+------+
需要将val1和val4组合成一个新列val，每列都有一行，以便输出如下所示。
注意： - 我的数据我有val1到val30 - ＆gt;即。每行30列，需要转换为行。
+----+------+--------+
| id | loc | val |
+----+------+--------+
| 1 | loc1 | 10 |
| 1 | loc1 | 190 |
| 1 | loc1 | null |
| 1 | loc1 | 20 |
| 2 | loc2 | 20 |
| 2 | loc2 | null |
| 2 | loc2 | 10 |
| 2 | loc2 | 10 |
+----+------+--------+
答案 0 :(得分：1)
您可以使用cross join generate_series来实现此目的：
select
id,
loc,
case x.i
when 1 then val1
when 2 then val2
. . .
end as val
from t
cross join generate_series(1, 4) x (i)
它只使用一次表格，可以轻松扩展以容纳更多列。
注意 ：在接受的答案中，第一种方法多次读取表格（与未转用的列一样多次），第二种方法错误postgresql中没有UNPIVOT。
答案 1 :(得分：1)
您可以将横向连接用于变换列到行：
rootType如果您希望使用动态添加列：
package com.holi.jackson;
import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonIgnoreType;
import com.fasterxml.jackson.annotation.JsonView;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.Version;
import com.fasterxml.jackson.databind.Module;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.introspect.Annotated;
import com.fasterxml.jackson.databind.introspect.NopAnnotationIntrospector;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.databind.ser.impl.SimpleFilterProvider;
import com.jayway.jsonassert.JsonAssert;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import static com.fasterxml.jackson.annotation.PropertyAccessor.FIELD;
import static com.fasterxml.jackson.databind.SerializationFeature.FAIL_ON_EMPTY_BEANS;
import static com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter.serializeAllExcept;
import static org.hamcrest.Matchers.hasSize;
import static org.junit.jupiter.api.Assertions.assertEquals;
/**
* Created by holi on 3/20/17.
*/
public class Jackson2SerializingFilteringTest {
private final User bob = new User("bob", "123456", "bob@example.com");
private final ObjectMapper jackson2 = new ObjectMapper();
@BeforeEach
void configure() {
jackson2.registerModules(configuration());
//write {} for empty bean
jackson2.disable(FAIL_ON_EMPTY_BEANS);
jackson2.setFilterProvider(serializeAll());
jackson2.setVisibility(FIELD, Visibility.ANY);
}
private Module configuration() {
return new SimpleModule() {
@Override
public void setupModule(SetupContext context) {
context.insertAnnotationIntrospector(filterIdAsClassName());
}
};
}
private NopAnnotationIntrospector filterIdAsClassName() {
return new NopAnnotationIntrospector() {
@Override
public Object findFilterId(Annotated ann) {
return ann.getRawType().getName();
}
@Override
public Version version() {
return super.version();
}
};
}
private SimpleFilterProvider serializeAll() {
SimpleFilterProvider filters = new SimpleFilterProvider();
//serialize all if filter not found,rather than throws an exception
filters.setFailOnUnknownId(false);
return filters;
}
@Test
void serializingAll() throws JsonProcessingException {
String json = jackson2.writer().writeValueAsString(bob);
JsonAssert.with(json)
.assertThat("$[*]", hasSize(3))
.assertEquals("name", bob.name)
.assertEquals("password", bob.password)
.assertEquals("mail", bob.mail);
}
@Test
void serializingAllExceptIgnoredProperties() throws JsonProcessingException {
@JsonIgnoreProperties({"name", "version"})
class JSONRoot {
String name = "jackson";
String version = "2.0";
}
JSONRoot root = new JSONRoot();
String json = jackson2.writer().writeValueAsString(root);
assertEquals("{}", json);
}
@Test
void serializingAllExceptIgnoredProperty() throws JsonProcessingException {
class JSONRoot {
String name = "jackson";
@JsonIgnore
String version = "2.0";
}
JSONRoot root = new JSONRoot();
String json = jackson2.writer().writeValueAsString(root);
JsonAssert.with(json)
.assertThat("$[*]", hasSize(1))
.assertEquals("name", root.name);
}
@Test
void serializingAllExceptIgnoredType() throws JsonProcessingException {
@JsonIgnoreType
class Ignored {
}
class JSONRoot {
Ignored ignored = new Ignored();
}
String json = jackson2.writer().writeValueAsString(new JSONRoot());
assertEquals("{}", json);
}
@Test
void serializingMixInAnnotations() throws JsonProcessingException {
jackson2.addMixIn(User.class, ExcludingMail.class);
String json = jackson2.writer().writeValueAsString(bob);
JsonAssert.with(json)
.assertThat("$[*]", hasSize(2))
.assertEquals("name", bob.name)
.assertEquals("password", bob.password);
}
@Test
void serializingUseFiltersToExcludingProperties() throws JsonProcessingException {
String json = jackson2.writer(excludes("password")).writeValueAsString(bob);
JsonAssert.with(json)
.assertThat("$[*]", hasSize(2))
.assertEquals("name", bob.name)
.assertEquals("mail", bob.mail);
}
@Test
void serializingRootTypePropertiesOnly() throws JsonProcessingException {
String json = jackson2.writerFor(Contactable.class).writeValueAsString(bob);
JsonAssert.with(json)
.assertThat("$[*]", hasSize(1))
.assertEquals("mail", bob.mail);
}
@Test
void serializingViewPropertiesOnly() throws JsonProcessingException {
String json = jackson2.writerWithView(Public.class).writeValueAsString(bob);
JsonAssert.with(json)
.assertThat("$[*]", hasSize(2))
.assertEquals("name", bob.name)
.assertEquals("mail", bob.mail);
}
private SimpleFilterProvider excludes(String... propertyNames) {
SimpleFilterProvider filters = serializeAll();
filters.addFilter(User.class.getName(), serializeAllExcept(propertyNames));
return filters;
}
private class User implements Contactable {
final String name;
@JsonView(Privacy.class)
String password;
@JsonView(Public.class)
final String mail;
public User(String name, String password, String mail) {
this.name = name;
this.password = password;
this.mail = mail;
}
public String getMail() {
return mail;
}
}
@interface Public {
}
@interface Privacy {
}
private interface Contactable {
String getMail();
}
@JsonIgnoreProperties("mail")
private class ExcludingMail {
}
}
请查看此链接以获取更多详细信息：Columns to rows
答案 2 :(得分：0)
我确信这是一种比这更优雅的方法。
SELECT * FROM (
select id, loc, val1 as val from #t a
UNION ALL
select id, loc, val2 as val from #t a
UNION ALL
select id, loc, val3 as val from #t a
UNION ALL
select id, loc, val4 as val from #t a
) x
order by ID
这是我尝试使用unpivot，但无法获取空值，也许是为空值执行连接？无论如何我还是会尝试
SELECT *
FROM (
SELECT * FROM #t
) main
UNPIVOT (
new_val
FOR val IN (val1, val2, val3, val4)
) unpiv
答案 3 :(得分：0)
根据用户需要，它不适用于postgress。看到评论中提到它。
我正在寻找一种处理＆＃34; NULL＆＃34;
的方法select p.id,p.loc,CASE WHEN p.val=0 THEN NULL ELSE p.val END AS val
from
(
SELECT id,loc,ISNULL(val1,0) AS val1,ISNULL(val2,0) AS val2,ISNULL(val3,0) AS val3,ISNULL(val4,0) AS val4
FROM Table1
)T
unpivot
(
val
for locval in(val1,val2,val3,val4)
)p
<强> 编辑：
我方面的最佳解决方案：
select a.id,a.loc,ex.val
from (select 'val1' as [over] union all select 'val2' union all select 'val3'
union all select 'val1' ) pmu
cross join (select id,loc from Table1) as a
left join
Table1 pt
unpivot
(
[val]
for [over] in (val1, val2, val3, val4)
) ex
on pmu.[over] = ex.[over] and
a.id = ex.id