2, simple query: (DQL)

• Syntax:

  select a name field, 2 field names, field names 3, ... from the table name:

  prompt:

  1. any sql statement to a ":" at the end.

  2. sql statement is not case sensitive.

• Query annual salary of employees? (Field can participate in math.)

  • select ename，sal *12 from emp：

    enmae: name

    sal: monthly salary

• Query results are listed rename?

  • select ename，sal *12 as yearsal from emp：

    yearsal: Rename salary

• There are Chinese alias?

  • select ename, sal * 12 as annual salary from emp: // Error

  • select ename, sal * 12 as 'salary' from emp: // correct

    note:

    Sql statement using standard single quotes. Although mysql support double quotes, try not to use.

    as keywords can be omitted

• A query field

  • ename from emp the SELECT: \ query the employee's name

• Query two fields

  • select empno, ename from emp: \ query the number of employees Name

    Query multiple fields, select the text can be separated by a comma, the last field, that is, from the front of the field can not use a comma.

• All Fields query

  • select * from emp: // actual development * not recommended, under development efficiency.