Query advanced alias

13.8　 Use alias to query data

MySQL It supports specifying aliases for field names or table names when querying data , When specifying aliases, you can use AS keyword , You can also not use .

13.8.1　 Specify an alias for the field name

The syntax format of specifying an alias for a field name is as follows ：

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SELECT column1 [AS] col1 [, column2 [AS] col2, … , columnn [AS] coln] FROM table_name

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among ,AS Keywords can be omitted .

Inquire about t_goods In the data table t_category_id and t_category Field data .

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mysql> SELECT t_category_id categoryId, t_category AS categoryName FROM t_goods;+---------------+----------------+| t_categoryId | categoryName   |+---------------+----------------+|              1 |  Women's wear / Women's Boutique   ||              1 |  Women's wear / Women's Boutique   ||              1 |  Women's wear / Women's Boutique   ||              1 |  Women's wear / Women's Boutique   ||              1 |  Women's wear / Women's Boutique   ||              1 |  Women's wear / Women's Boutique   ||              2 |  Outdoor sports         ||              2 |  Outdoor sports         ||              2 |  Outdoor sports         ||              2 |  Outdoor sports         ||              2 |  Outdoor sports         ||              2 |  Outdoor sports         |+---------------+----------------+12 rows in set (0.00 sec)

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The result shows that the data is correctly queried . thus it can be seen , Use AS Keywords and not used AS Keywords can specify aliases for fields . When specifying an alias for a field , The field names in the query result data list show aliases ; Otherwise, the field name is displayed .

13.8.2　 Specify an alias for the table name

The syntax format of specifying aliases for table names is as follows ：

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SELECT * FROM table_name [AS] tableName

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perhaps

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SELECT column1 [, column2, … , columnn] FROM table_name [AS] tableName

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among ,AS Keywords can be omitted .

Query by specifying an alias for the data table t_goods In the data table t_name Fields and t_stock Field data .

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mysql> SELECT t_name, t_stock FROM t_goods goods;+--------------+---------+| t_name        | t_stock |+--------------+---------+| T T-shirt           |   1000  ||  dress         |   2500  ||  fleece           |   1500  ||  A pair of jeans         |   3500  ||  Pleated skirt         |    500  ||  Woolen coat       |   1200  ||  Bicycle         |   1000  ||  Mountain Bike     |   2500  ||  Alpenstocks         |   1500  ||  Riding equipment       |   3500  ||  Outdoor sports coat  |    500  ||  Skate           |   1200  |+--------------+---------+12 rows in set (0.00 sec)

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13.8.3　 Specify aliases for both field names and table names

The syntax format of specifying aliases for both field names and table names is as follows ：

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SELECT column1 [AS] col1 [, column2 [AS] col2, … , columnn [AS] coln] FROM table_name [AS] tableName

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among ,AS Keywords can be omitted .

Inquire about t_goods In the data table t_name Field 、t_price Fields and t_upper_time Field data .

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mysql> SELECT     -> t_name name, t_price AS price, t_upper_time upperTime    -> FROM t_goods AS goods;+-------------+---------+---------------------+| name        |  price  | uppertime           |+-------------+---------+---------------------+| T T-shirt          |   39.90 | 2020-11-10 00:00:00 ||  dress       |   79.90 | 2020-11-10 00:00:00 ||  fleece         |   79.90 | 2020-11-10 00:00:00 ||  A pair of jeans       |   89.90 | 2020-11-10 00:00:00 ||  Pleated skirt       |   29.90 | 2020-11-10 00:00:00 ||  Woolen coat     |  399.90 | 2020-11-10 00:00:00 ||  Bicycle       |  399.90 | 2020-11-10 00:00:00 ||  Mountain Bike   | 1399.90 | 2020-11-10 00:00:00 ||  Alpenstocks       |   59.90 | 2020-11-10 00:00:00 ||  Riding equipment     |  399.90 | 2020-11-10 00:00:00 ||  Outdoor sports coat  |  799.90 | 2020-11-10 00:00:00 ||  Skate         |  499.90 | 2020-11-10 00:00:00 |+-------------+---------+---------------------+12 rows in set (0.00 sec)

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Be careful ： Specify an alias for a field or table , It is often used in multi table associative queries .