Mysql (7) in-depth select query _ MySQL

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Mysql (7) in-depth select query

Related links:

Mysql (1) installation of mysql

Http: // database/201210/162314 .html;

Mysql-related operations (2)

Http: // database/201210/162315 .html;

Mysql operations on data tables (3)

Http: // database/201210/162316 .html;

Mysql (4) Data Table query operations

Http: // database/201210/162317 .html;

Mysql operations (5)

Http: // database/201210/162318 .html;

Mysql (6) string pattern matching

Http: // database/201210/163969 .html

I. table alias

SELECT * FROM pet p order by p. age;

This is to sort the queried data by the table's age.

If you want to pair a pet in a pet table, you can use the alias of the table as follows:

SELECT p1.name, p1.sex, p2, name, p2.sex FROM pet AS p1, pet AS p2 WHERE p1.species = p2.species AND p1.sex = "M" AND p2.sex = "F ";

This statement means pairing by species, with the gender M and F;

II. column alias

Query the pet name and type (directly reference the column name ).

SELECT name, species FROM pet order by name, species;

Similar:

SELECT name, species FROM pet order by 1, 2;

This is the same as the above functions.

You can also name a column.

SELECT name AS n, species AS s FROM pet order by n, s;

This function is the same as the preceding statement.

Use the column alias in the clause:

SELECT species, COUNT (*) AS total FROM pet group by species HAVING total> 1;

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