使用 WHERE 进行 SELECT

在本主题中，我们将基于此用户表：

CREATE TABLE sch_test.user_table
(
  id serial NOT NULL,
  username character varying,
  pass character varying,
  first_name character varying(30),
  last_name character varying(30),
  CONSTRAINT user_table_pkey PRIMARY KEY (id)
)

+----+------------+-----------+----------+------+
| `id` | first_name | last_name | username | pass |   
+----+------------+-----------+----------+------+
| `1`  | hello      | world     | hello    | word |   
+----+------------+-----------+----------+------+
| `2`  | root       | me        | root     | toor |   
+----+------------+-----------+----------+------+

句法

选择每件事：

SELECT * FROM schema_name.table_name WHERE <condition>;

选择一些字段：

SELECT field1, field2 FROM schema_name.table_name WHERE <condition>;

例子

-- SELECT every thing where id = 1
SELECT * FROM schema_name.table_name WHERE id = 1;

-- SELECT id where username = ? and pass = ?
SELECT id FROM schema_name.table_name WHERE username = 'root' AND pass = 'toor';

-- SELECT first_name where id not equal 1
SELECT first_name FROM schema_name.table_name WHERE id != 1;