The difference between Union & Union All in SQL Server/pOSTGRESQL

Following is test in SQL Server:

USE [TestDB]
CREATE TABLE [dbo].[UserInfoTest02](
    [number] [bigint] NOT NULL,
    [name] [varchar](20) NOT NULL,
    [age] [int] NOT NULL,
    [sex] [bit] NOT NULL,
    [address] [varchar](200) NULL
)

CREATE TABLE [dbo].[UserInfoTest03](
    [number] [bigint] NOT NULL,
    [name] [varchar](20) NOT NULL,
    [age] [int] NOT NULL,
    [sex] [bit] NOT NULL,
    [address] [varchar](200) NULL
)

CREATE TABLE [dbo].[UserInfoTest04](
    [SID] [bigint] NOT NULL,
    [name] [varchar](20) NOT NULL,
    [age] [int] NOT NULL,
    [sex] [bit] NOT NULL,
    [address] [varchar](200) NULL
)

Insert into UserInfoTest02
(number,name,age,sex,address)
Values
(1, 'A',12,0,'A'),
(2, 'B',12,0,'A')

Insert into UserInfoTest03
(number,name,age,sex,address)
Values
(1, 'A',12,0,'A'),
(2, 'B',12,0,'BB')

Insert into UserInfoTest04
(SID,name,age,sex,address)
Values
(1, 'A',12,0,'A'),
(2, 'B',12,0,'BB')

SELECT SID, name,age,sex,address
FROM UserInfoTest04
UNION ALL
SELECT number,name,age,sex,address
FROM UserInfoTest02

--Test Result1

SID    name    age    sex    address
1    A    12    0    A
2    B    12    0    BB
1    A    12    0    A
2    B    12    0    A

SELECT SID, name,age,sex,address
FROM UserInfoTest04
UNION
SELECT number,name,age,sex,address
FROM UserInfoTest02

--Test Result2

SID    name    age    sex    address
1    A    12    0    A
2    B    12    0    A
2    B    12    0    BB

SELECT number, name,age,sex,address
FROM UserInfoTest03
UNION
SELECT number,name,age,sex,address
FROM UserInfoTest02

--Test Result3

number    name    age    sex    address
1    A    12    0    A
2    B    12    0    A
2    B    12    0    BB

Test in Postgresql:

INSERT INTO "Test01"("SID", "Name") VALUES (1, 'A');
INSERT INTO "Test01"("SID", "Name") VALUES (2, 'B');
INSERT INTO "Test01"("SID", "Name") VALUES (3, 'C');

INSERT INTO "Test02"("SID", "Name") VALUES (1, 'A');
INSERT INTO "Test02"("SID", "Name") VALUES (2, 'B');

INSERT INTO "Test03"("Number", "address") VALUES(1, 'A');
INSERT INTO "Test03"("Number", "address") VALUES(2, 'B');

SELECT "SID", "Name" FROM "Test01"
UNION ALL
SELECT "SID", "Name" FROM "Test02";

--Test Result1:

1;"A"
2;"B"
3;"C"
1;"A"
2;"B"

SELECT "SID", "Name" FROM "Test01"
UNION
SELECT "Number", "address" FROM "Test03";

--Test Result2:

2;"B"
1;"A"
3;"C"