Simple tutorial on SQL statements in linux --- UNION, simple tutorial --- union

Simple tutorial on SQL statements in linux --- UNION, simple tutorial --- union

UNIONThe purpose of the command is to combine the results of two SQL statements. From this perspective,UNIONThis is somewhat similar to JOIN, because both commands can retrieve data from multiple tables.UNIONOne restriction is that the columns generated by two SQL statements must be of the same data type. In addition, when we useUNIONIn this command, we only see different data values (similarSELECT DISTINCT).

UNIONSyntax:

[SQL statement 1]
UNION
[SQL statement 2];

Suppose we have two tables,

Store_InformationTable

Store_Name	Sales	Txn_Date
Los Angeles	1500	05-Jan 1999
San Diego	250	07-Jan-1999
Los Angeles	300	08-Jan 1999
Boston	700	08-Jan 1999

Internet SalesTable

Txn_Date	Sales
07-Jan-1999	250
10-Jan 1999	535
11-Jan 1999	320
12-Jan 1999	750

We need to find out all the days with a turnover. To achieve this goal, we use the following SQL statement:

SELECT Txn_Date FROM Store_Information
UNION
SELECT Txn_Date FROM Internet_Sales;

Result:

Txn_Date

Jan-05-1999

Jan-07-1999

Jan-08-1999

Jan-10-1999

Jan-11-1999

Jan-12-1999

It is worth noting that if we useSelect distinct Txn_DateThen we will get the same result.

Linux test results:

1. Create a table

2. Insert table records

3. UNION (and) two tables