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This article mainly explains "how mysql queries data and aliases". The explanation content in this article is simple and clear, easy to learn and understand. Please follow the ideas of Xiaobian to study and learn "how mysql queries data and aliases" together.

In mysql, you can query data and alias it using the SELECT statement and the AS keyword, with the syntax SELECT field name/* FROM table name AS table alias; or SELECT field name AS field alias FROM data table name;.

Operating environment of this tutorial: Windows 7 system, MySQL8 version, Dell G3 computer.

Specify aliases for tables

When the table name is long or when special queries are performed, you can specify an alias for the table to replace the original name of the table for convenience.

The basic syntax for assigning aliases to tables is:

[AS]

The meaning of each clause is as follows:

: The name of the data table stored in the database.

: The new name of the table specified at query time.

The AS keyword can be omitted, and the table name and alias need to be separated by spaces after omission.

Note: A table alias cannot have the same name as another table in the database. Field aliases cannot have the same name as other fields in the table. The alias of a field cannot be used in a conditional expression, otherwise an error message such as ERROR 1054 (42S22): Unknown column will appear.

Example 1

The following alias stu is specified for the tb_students_info table

mysql> SELECT stu.name,stu.height FROM tb_students_info AS stu;+--------+--------+| name | height |+--------+--------+| Dany | 160 || Green | 158 || Henry | 185 || Jane | 162 || Jim | 175 || John | 172 || Lily | 165 || Susan | 170 || Thomas | 178 || Tom | 165 |+--------+--------+10 rows in set (0.04 sec)

Specify an alias for a field

When querying data using SELECT statements, MySQL displays the fields that specify output after each SELECT. Sometimes to make the results more intuitive, we can assign an alias to the field.

The basic syntax for assigning aliases to fields is:

[AS]

The grammatical meaning of each clause is as follows:

: The name defined for the field in the data table.

: New name for field.

The AS keyword can be omitted, and the field name and alias need to be separated by spaces after omission.

Example 2

Query the tb_students_info table, specifying the alias student_name for name and student_age for age

mysql> SELECT name AS student_name, age AS student_age FROM tb_students_info;+--------------+-------------+| student_name | student_age |+--------------+-------------+| Dany | 25 || Green | 23 || Henry | 23 || Jane | 22 || Jim | 24 || John | 21 || Lily | 22 || Susan | 23 || Thomas | 22 || Tom | 23 |+--------------+-------------+10 rows in set (0.00 sec)

Note: Table aliases are used only when executing queries and are not displayed in the returned results. After the alias is defined for the field, it will be returned to the client for display. The displayed field is the alias of the field.

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