Query data

Use the SELECT statement to query data from a table.

Example:

Create Table a that contains the following data:

obclient> CREATE TABLE a (id int, name varchar(50), num int);
Query OK, 0 rows affected (0.07 sec)

obclient> INSERT INTO a VALUES(1,'a',100),(2,'b',200),(3,'a',50);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

obclient> SELECT * FROM a;
+------+------+------+
| ID   | NAME | NUM  |
+------+------+------+
|    1 | a    |  100 |
|    2 | b    |  200 |
|    3 | a    |   50 |
+------+------+------+
3 rows in set (0.00 sec)

1. Query the data in the name field from Table a.

   obclient> SELECT name FROM a;
   +------+
   | NAME |
   +------+
   | a    |
   | b    |
   | a    |
   +------+
   3 rows in set (0.00 sec)
   

2. Deduplicate the query results of the name field.

   obclient> SELECT DISTINCT name FROM a;
   +------+
   | NAME |
   +------+
   | a    |
   | b    |
   +------+
   2 rows in set (0.00 sec)
   

3. Return the values of the corresponding id, name, and num fields based on the filtering condition name = 'a'.

   obclient> SELECT id, name, num FROM a WHERE name = 'a';
   +------+------+------+
   | ID   | NAME | NUM  |
   +------+------+------+
   |    1 | a    |  100 |
   |    3 | a    |   50 |
   +------+------+------+
   2 rows in set (0.01 sec)
   

For more information on the syntax of the SELECT statement, see the "SELECT" topic in SQL Reference (Oracle Mode).