openGauss学习笔记-13 openGauss 简略数据管理-DELETE句子13.1 语法格局13.2 参数阐明13.3 示例
openGauss学习笔记-13 openGauss 简略数据管理-DELETE句子
DELETE句子可以从指定的表里删去满足WHERE子句的行。假如WHERE子句不存在,将删去表中所有行,效果只保存表结构。
13.1 语法格局
DELETE FROM table_name
[WHERE condition];
13.2 参数阐明
-
table_name
方针表的称谓(可以有方式润饰)。
取值规划:已存在的表名。
-
condition
一个返回Boolean值的表达式,用于判断哪些行需求被删去。
13.3 示例
创立表customer_t1_bak,表的结构、数据与customer_t1共同。
openGauss=# CREATE TABLE customer_t1_bak AS TABLE customer_t1;
INSERT 0 9
创立的表customer_t1_bak,数据如下:
openGauss=# SELECT * FROM customer_t1_bak;
c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
---------------+---------------+--------------+-------------+--------
3869 | hello | Grace | | 1000
3869 | hello | Grace | | 1000
3869 | | Grace | |
3869 | hello | | |
3869 | hello | | |
| | | |
6985 | maps | Joes | | 2200
9976 | world | James | | 5000
4421 | Admin | Local | | 3000
(9 rows)
实行如下句子删去customer_t1_bak中c_customer_sk等于3869的职工。
openGauss=# DELETE FROM customer_t1_bak WHERE c_customer_sk = 3869;
DELETE 5
得到的效果如下,可以看到c_customer_sk = 3869的行已经被删去。
openGauss=# SELECT * FROM customer_t1_bak;
c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
---------------+---------------+--------------+-------------+--------
| | | |
6985 | maps | Joes | | 2200
9976 | world | James | | 5000
4421 | Admin | Local | | 3000
(4 rows)
不指定WHERE句子时,默许删去整张表的数据,仅保存表结构。
openGauss=# DELETE FROM customer_t1_bak;
DELETE 4
得到效果如下。
openGauss=# SELECT * FROM customer_t1_bak;
c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
---------------+---------------+--------------+-------------+--------
(0 rows)
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