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This article mainly introduces how to use SELECT and SELECT* sentences in SQL, which has a certain reference value, and interested friends can refer to it. I hope you will gain a lot after reading this article.

SQL SELECT statement

The SELECT statement is used to select data from a table, and the results are stored in a result table (called a result set). Syntax:

SELECT column name FROM table name SELECT * FROM table name

Note: SQL statements are not case-sensitive. SELECT is equivalent to select.

SQL SELECT instance

To get the contents of columns named "LastName" and "FirstName", use SELECT statements like this:

SELECT LastName,FirstName FROM Persons

"Persons" table:

Id LastName FirstName Address City1 Adams John Oxford Street London2 Bush George Fifth Avenue New York3 Carter Thomas Changan Street Beijing

Result table (result set):

LastName FirstNameAdams JohnBush GeorgeCarter Thomas

SQL SELECT * instance

Now we want to select all the columns from the "Persons" table. Replace the column name with the symbol *, like this:

SELECT * FROM Persons

Result table (result set):

Id LastName FirstName Address City1 Adams John Oxford Street London2 Bush George Fifth Avenue New York3 Carter Thomas Changan Street Beijing

Tip: an asterisk (*) is a shortcut to select all columns.

SQL SELECT DISTINCT statement

Duplicate values may be included in the table, and sometimes you may want to list only different (distinct) values.

The keyword DISTINCT is used to return a unique different value. The syntax is as follows:

SELECT DISTINCT column name FROM table name

Use the DISTINCT keyword

To select only a unique different value from the Company column, we need to use the SELECT DISTINCT statement:

SELECT DISTINCT Company FROM Orders

"Orders" table:

Company OrderNumberIBM 3532HuluMiao 2356Apple 4698IBM 6953

Results:

CompanyIBMHuluMiaoApple

Note: "IBM" is listed only once in the result set. If you use the SELECT statement directly, it will be listed twice.

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