DATABASE2 MySQL - 11.SELECT - egoing

mysql> DESC topic;
+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| id          | int          | NO   | PRI | NULL    | auto_increment |
| title       | varchar(100) | NO   |     | NULL    |                |
| description | text         | YES  |     | NULL    |                |
| created     | datetime     | NO   |     | NULL    |                |
| author      | varchar(30)  | YES  |     | NULL    |                |
| profile     | varchar(100) | YES  |     | NULL    |                |
+-------------+--------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

mysql> SELECT * FROM topic
    -> ;
+----+------------+-------------------+---------------------+--------+---------------------------+
| id | title      | description       | created             | author | profile                   |
+----+------------+-------------------+---------------------+--------+---------------------------+
|  1 | MySQL      | MySQL is ...      | 2021-10-13 19:58:34 | egoing | developer                 |
|  2 | ORCALE     | ORCALE is ...     | 2021-10-13 20:13:20 | egoing | developer                 |
|  3 | SQL Server | SQL Server is ... | 2021-10-13 20:13:28 | duru   | database administrator    |
|  4 | PostgreSQL | PostgreSQL is ... | 2021-10-13 20:13:35 | taeho  | data sicentist, developer |
|  5 | MongoDB    | MongoDB is ...    | 2021-10-13 20:13:40 | egoing | developer                 |
+----+------------+-------------------+---------------------+--------+---------------------------+
5 rows in set (0.00 sec)

mysql> SELECT id FROM topic
    -> ;
+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
+----+
5 rows in set (0.00 sec)

mysql> SELECT description FROM topic;
+-------------------+
| description       |
+-------------------+
| MySQL is ...      |
| ORCALE is ...     |
| SQL Server is ... |
| PostgreSQL is ... |
| MongoDB is ...    |
+-------------------+
5 rows in set (0.00 sec)

mysql> DESC topic;
+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| id          | int          | NO   | PRI | NULL    | auto_increment |
| title       | varchar(100) | NO   |     | NULL    |                |
| description | text         | YES  |     | NULL    |                |
| created     | datetime     | NO   |     | NULL    |                |
| author      | varchar(30)  | YES  |     | NULL    |                |
| profile     | varchar(100) | YES  |     | NULL    |                |
+-------------+--------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

mysql> SELECT "egong";
+-------+
| egong |
+-------+
| egong |
+-------+
1 row in set (0.00 sec)

mysql> SELECT "egoing",1+1
    -> ;
+--------+-----+
| egoing | 1+1 |
+--------+-----+
| egoing |   2 |
+--------+-----+
1 row in set (0.00 sec)

mysql> SELECT *;
ERROR 1096 (HY000): No tables used
mysql> SELECT * FROM topic;
+----+------------+-------------------+---------------------+--------+---------------------------+
| id | title      | description       | created             | author | profile                   |
+----+------------+-------------------+---------------------+--------+---------------------------+
|  1 | MySQL      | MySQL is ...      | 2021-10-13 19:58:34 | egoing | developer                 |
|  2 | ORCALE     | ORCALE is ...     | 2021-10-13 20:13:20 | egoing | developer                 |
|  3 | SQL Server | SQL Server is ... | 2021-10-13 20:13:28 | duru   | database administrator    |
|  4 | PostgreSQL | PostgreSQL is ... | 2021-10-13 20:13:35 | taeho  | data sicentist, developer |
|  5 | MongoDB    | MongoDB is ...    | 2021-10-13 20:13:40 | egoing | developer                 |
+----+------------+-------------------+---------------------+--------+---------------------------+
5 rows in set (0.00 sec)

mysql> SELECT "egoing";
+--------+
| egoing |
+--------+
| egoing |
+--------+
1 row in set (0.00 sec)

mysql> SELECT "egoing",1+1;
+--------+-----+
| egoing | 1+1 |
+--------+-----+
| egoing |   2 |
+--------+-----+
1 row in set (0.00 sec)

mysql> SELECT id,title,description,created,author FROM topic WHERE author='egoing';
+----+---------+----------------+---------------------+--------+
| id | title   | description    | created             | author |
+----+---------+----------------+---------------------+--------+
|  1 | MySQL   | MySQL is ...   | 2021-10-13 19:58:34 | egoing |
|  2 | ORCALE  | ORCALE is ...  | 2021-10-13 20:13:20 | egoing |
|  5 | MongoDB | MongoDB is ... | 2021-10-13 20:13:40 | egoing |
+----+---------+----------------+---------------------+--------+
3 rows in set (0.00 sec)

mysql> SELECT "egoing",4;
+--------+---+
| egoing | 4 |
+--------+---+
| egoing | 4 |
+--------+---+
1 row in set (0.00 sec)

mysql> SELECT "egoing",5*5;
+--------+-----+
| egoing | 5*5 |
+--------+-----+
| egoing |  25 |
+--------+-----+
1 row in set (0.00 sec)

mysql> SELECT "duru",2+1;
+------+-----+
| duru | 2+1 |
+------+-----+
| duru |   3 |
+------+-----+
1 row in set (0.00 sec)

mysql> SELECT * FROM topic;
+----+------------+-------------------+---------------------+--------+---------------------------+
| id | title      | description       | created             | author | profile                   |
+----+------------+-------------------+---------------------+--------+---------------------------+
|  1 | MySQL      | MySQL is ...      | 2021-10-13 19:58:34 | egoing | developer                 |
|  2 | ORCALE     | ORCALE is ...     | 2021-10-13 20:13:20 | egoing | developer                 |
|  3 | SQL Server | SQL Server is ... | 2021-10-13 20:13:28 | duru   | database administrator    |
|  4 | PostgreSQL | PostgreSQL is ... | 2021-10-13 20:13:35 | taeho  | data sicentist, developer |
|  5 | MongoDB    | MongoDB is ...    | 2021-10-13 20:13:40 | egoing | developer                 |
+----+------------+-------------------+---------------------+--------+---------------------------+
5 rows in set (0.00 sec)

mysql> SELECT "egoing",1+1
    -> ;
+--------+-----+
| egoing | 1+1 |
+--------+-----+
| egoing |   2 |
+--------+-----+
1 row in set (0.00 sec)

mysql> SELECT 1+1;
+-----+
| 1+1 |
+-----+
|   2 |
+-----+
1 row in set (0.00 sec)

mysql> SELECT id,title,description,created,author FROM topic WHERE author='egoing' ORDER BY id DESC;
+----+---------+----------------+---------------------+--------+
| id | title   | description    | created             | author |
+----+---------+----------------+---------------------+--------+
|  5 | MongoDB | MongoDB is ... | 2021-10-13 20:13:40 | egoing |
|  2 | ORCALE  | ORCALE is ...  | 2021-10-13 20:13:20 | egoing |
|  1 | MySQL   | MySQL is ...   | 2021-10-13 19:58:34 | egoing |
+----+---------+----------------+---------------------+--------+
3 rows in set (0.00 sec)

mysql> SELECT id,title,description,created,author FROM topic WHERE author='egoing' ORDER BY created DESC;
+----+---------+----------------+---------------------+--------+
| id | title   | description    | created             | author |
+----+---------+----------------+---------------------+--------+
|  5 | MongoDB | MongoDB is ... | 2021-10-13 20:13:40 | egoing |
|  2 | ORCALE  | ORCALE is ...  | 2021-10-13 20:13:20 | egoing |
|  1 | MySQL   | MySQL is ...   | 2021-10-13 19:58:34 | egoing |
+----+---------+----------------+---------------------+--------+
3 rows in set (0.00 sec)

mysql> SELECT id,title,description,created,author FROM topic WHERE author='egoing' ORDER BY id DESC LIMIT 2;
+----+---------+----------------+---------------------+--------+
| id | title   | description    | created             | author |
+----+---------+----------------+---------------------+--------+
|  5 | MongoDB | MongoDB is ... | 2021-10-13 20:13:40 | egoing |
|  2 | ORCALE  | ORCALE is ...  | 2021-10-13 20:13:20 | egoing |
+----+---------+----------------+---------------------+--------+
2 rows in set (0.00 sec)

mysql> SELECT id,title,description,created,author FROM topic WHERE author='egoing' ORDER BY id DESC LIMIT 2;
+----+---------+----------------+---------------------+--------+
| id | title   | description    | created             | author |
+----+---------+----------------+---------------------+--------+
|  5 | MongoDB | MongoDB is ... | 2021-10-13 20:13:40 | egoing |
|  2 | ORCALE  | ORCALE is ...  | 2021-10-13 20:13:20 | egoing |
+----+---------+----------------+---------------------+--------+
2 rows in set (0.00 sec)

mysql> SELECT * FROM topic LIMIT 3;
+----+------------+-------------------+---------------------+--------+------------------------+
| id | title      | description       | created             | author | profile                |
+----+------------+-------------------+---------------------+--------+------------------------+
|  1 | MySQL      | MySQL is ...      | 2021-10-13 19:58:34 | egoing | developer              |
|  2 | ORCALE     | ORCALE is ...     | 2021-10-13 20:13:20 | egoing | developer              |
|  3 | SQL Server | SQL Server is ... | 2021-10-13 20:13:28 | duru   | database administrator |
+----+------------+-------------------+---------------------+--------+------------------------+
3 rows in set (0.00 sec)

mysql>

 

 

mysql> SELECT "egoing",1+1
    -> ;
+--------+-----+
| egoing | 1+1 |
+--------+-----+
| egoing |   2 |
+--------+-----+
1 row in set (0.00 sec)

 

#이 부분이 이해가 잘 안된다. 어째서 바로 아래행에 2가 나오는 것인지.