Simple tutorial on SQL statements in linux-simple tutorial on functions and SQL

Simple tutorial on SQL statements in linux-simple tutorial on functions and SQL

Since there are a lot of data in the database that already has numbers, a very important purpose is to be able to perform some operations on these numbers, such as sum them up, or find out their average value. SQL provides some such functions. They are:

• AVG(Average)
• COUNT(Count)
• MAX(Maximum)
• MIN(Minimum)
• SUM(Total)

The syntax for using functions is:

SELECT "function name" ("column name ")
FROM "table name ";

For example, if we want to find the sum of the Sales field in our example table,

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

Let's get,

Select sum (Sales) FROM Store_Information;

Result:

SUM (Sales)

2750

2750 represents the sum of all Sales positions: 1500 + 250 + 300 + 700.

In addition to the use of functions, SQL can also perform simple mathematical operations, such as addition (+) and subtraction (-). For text data, SQL also has several functions for text processing, such as text connection (Concatenation), Text trimming (Trim), And sub-string (Substring). Different databases have different syntaxes for these functions, so it is best to refer to the information of your database to determine how these functions are used in that database.

Linux has been tested as follows:

Reprinted, please note: Xiao Liu