How to query the value of two fields in mysql

In mysql, you can query the values ​​of two fields through the SELECT statement. The query syntax is "SELECT field name 1, field name 2 FROM data table name [WHERE clause];". The SELECT statement can obtain data under multiple fields. You only need to specify the field name to be searched after the keyword SELECT. Different field names can be separated by commas ","; the "WHERE clause" is optional , used to set query conditions. If this item is set, the query data will be limited to meet the query conditions.

The operating environment of this tutorial: windows7 system, mysql8 version, Dell G3 computer.

In mysql, you can use the SELECT statement to query the values ​​of two fields.

The SELECT statement can obtain data under multiple fields. You only need to specify the field name to be searched after the keyword SELECT. Different field names are separated by commas ",", and the last one There is no need to add a comma after the field.

The syntax for querying two fields is:

SELECT 字段名1,字段名2 FROM 数据表名 [WHERE子句];

• The field name after the SELECT keyword is the field that needs to be searched, so you only need to The names of the two fields in the table that need to be queried follow the SELECT keyword.

• WHERE clause: It is optional. If this item is selected, the query data must meet the query conditions.

Example: Get the values ​​of the id and name fields from the tb_students_info table

mysql> SELECT id,name FROM tb_students_info;

Output The result shows all the data under the id and name fields in the tb_students_info table.

Extended knowledge:

The field name after the SELECT keyword is the field that needs to be searched. Therefore, if you want to list all fields in the table, you can list all fields in the table. The name of the field follows the SELECT keyword.

Example: Query all data in the tb_students_info table

SELECT id,name,dept_id,age,sex,height,login_date FROM tb_students_info;

But sometimes, because the table has many fields, you may not be able to remember the names of all the fields. Therefore this method is very inconvenient.

Therefore, we can use "*" to query all fields of the table. Syntax:

SELECT * FROM 表名;

When using "*" to query, we can only query according to the fields in the data table. Arrange in order, and the order of fields cannot be changed.

In the above example, the data of all fields is queried from the tb_students_info table, which is:

mysql> SELECT * FROM tb_students_info;

The results show that when the "*" wildcard is used, all fields will be returned Columns, data columns are displayed in the order when the table is created.

Note: Generally, it is best not to use the wildcard character "*" unless you need to use all field data in the table. Although using wildcards can save time typing query statements, obtaining unnecessary column data often reduces the efficiency of the query and the application used. The advantage of using "*" is that when the names of the required columns are not known, they can be obtained via "*".

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