DELETE语句

DELETE语句可以从指定的表里删除满足WHERE子句的行。如果WHERE子句不存在，将删除表中所有行，结果只保留表结构。

语法格式

  1. DELETE FROM table_name 
  2.        [WHERE condition];

参数说明

  • table_name

    目标表的名称（可以有模式修饰）。

    取值范围：已存在的表名。

  • condition

    一个返回Boolean值的表达式，用于判断哪些行需要被删除。

示例

创建表customer_t1_bak，表的结构、数据与customer_t1一致。

  1. openGauss=# CREATE TABLE customer_t1_bak AS TABLE customer_t1;
  2. INSERT 0 9

创建的表customer_t1_bak，数据如下：

  1. openGauss=# SELECT * FROM customer_t1_bak;
  2.  c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
  3. ---------------+---------------+--------------+-------------+--------
  4.           3869 | hello         | Grace        |             |   1000
  5.           3869 | hello         | Grace        |             |   1000
  6.           3869 |               | Grace        |             |
  7.           3869 | hello         |              |             |
  8.           3869 | hello         |              |             |
  9.                |               |              |             |
  10.           6985 | maps          | Joes         |             |   2200
  11.           9976 | world         | James        |             |   5000
  12.           4421 | Admin         | Local        |             |   3000
  13. (9 rows)

执行如下语句删除customer_t1_bak中c_customer_sk等于3869的职员。

  1. openGauss=# DELETE FROM customer_t1_bak WHERE c_customer_sk = 3869;
  2. DELETE 5

得到的结果如下，可以看到c_customer_sk = 3869的行已经被删除。

  1. openGauss=# SELECT * FROM customer_t1_bak;
  2.  c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
  3. ---------------+---------------+--------------+-------------+--------
  4.                |               |              |             |
  5.           6985 | maps          | Joes         |             |   2200
  6.           9976 | world         | James        |             |   5000
  7.           4421 | Admin         | Local        |             |   3000
  8. (4 rows)

不指定WHERE语句时，默认删除整张表的数据，仅保留表结构。

  1. openGauss=# DELETE FROM customer_t1_bak;
  2. DELETE 4

得到结果如下。

  1. openGauss=# SELECT * FROM customer_t1_bak;
  2.  c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
  3. ---------------+---------------+--------------+-------------+--------
  4. (0 rows)