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数据库中update与delete使用表别名的深入研究

作者：SarPro

本文介绍了UPDATE和DELETE SQL语句在Oracle, SQLite, PostgreSQL, MYSQL, mariadb等数据库系统中的执行差异,文中通过代码介绍的非常详细,对数据库开发和维护人员有指导意义,需要的朋友可以参考下

总结

Update

SQL语句示例OracleSQLitePostgreSQLMYSQL & mariadb
UPDATE users as a SET a.age = 111 WHERE a.name = 'Alice';报错报错报错正常执行
UPDATE users as a SET a.age = 111 WHERE name = 'Alice';报错报错报错正常执行
UPDATE users as a SET age = 111 WHERE a.name = 'Alice';报错正常执行正常执行正常执行
UPDATE users as a SET age = 111 WHERE name = 'Alice';报错正常执行正常执行正常执行

Delete

SQL语句示例OracleSQLitePostgreSQLMYSQL & mariadb
delete from users as a WHERE a.name = 'Alice';报错报错报错报错
delete from users as a WHERE name = 'Alice';报错报错报错报错

1 Update

1.1 测试用例UPDATE users as a SET a.age = 111 WHERE a.name = 'Alice';

UPDATE users as a SET a.age = 111 WHERE a.name = 'Alice';

CREATE TABLE users (
    name VARCHAR(255) NOT NULL,
    age INT
);

INSERT INTO users (name, age) VALUES ('Alice', 25);
INSERT INTO users (name, age) VALUES ('Bob', 30);
INSERT INTO users (name, age) VALUES ('Charlie', 35);
INSERT INTO users (name, age) VALUES ('Alice', 40);

SELECT * FROM users;
UPDATE users as a SET a.age = 111 WHERE a.name = 'Alice';
SELECT * FROM users;

修改前表内容如下：

nameage
Alice25
Bob30
Charlie35
Alice40

1 ORACLE

执行报错

ORA-00971: missing SET keyword

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

2 sqlite

执行报错

Error: near line 12: near ".": syntax error

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

3 PG

执行报错

psql:commands.sql:12: ERROR:  column "a" of relation "users" does not exist
LINE 1: UPDATE users as a SET a.age = 111 WHERE a.name = 'Alice';

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

4 MYSQL & mariadb

执行正常

后表内容已经更新，如下：

nameage
Alice111
Bob30
Charlie35
Alice111

1.2 测试用例UPDATE users as a SET a.age = 111 WHERE name = 'Alice';

UPDATE users as a SET a.age = 111 WHERE name = 'Alice';

CREATE TABLE users (
    name VARCHAR(255) NOT NULL,
    age INT
);

INSERT INTO users (name, age) VALUES ('Alice', 25);
INSERT INTO users (name, age) VALUES ('Bob', 30);
INSERT INTO users (name, age) VALUES ('Charlie', 35);
INSERT INTO users (name, age) VALUES ('Alice', 40);

SELECT * FROM users;
UPDATE users as a SET a.age = 111 WHERE name = 'Alice';
SELECT * FROM users;

修改前表内容如下：

nameage
Alice25
Bob30
Charlie35
Alice40

1 ORACLE

执行报错

ORA-00971: missing SET keyword

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

2 sqlite

 执行报错

Error: near line 12: near ".": syntax error

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

3 PG

  执行报错

psql:commands.sql:12: ERROR:  column "a" of relation "users" does not exist
LINE 1: UPDATE users as a SET a.age = 111 WHERE name = 'Alice';

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

4 MYSQL & mariadb

执行正常

后表内容已经更新，如下：

nameage
Alice111
Bob30
Charlie35
Alice111

1.3 测试用例UPDATE users as a SET age = 111 WHERE a.name = 'Alice';

UPDATE users as a SET age = 111 WHERE a.name = 'Alice';

CREATE TABLE users (
    name VARCHAR(255) NOT NULL,
    age INT
);

INSERT INTO users (name, age) VALUES ('Alice', 25);
INSERT INTO users (name, age) VALUES ('Bob', 30);
INSERT INTO users (name, age) VALUES ('Charlie', 35);
INSERT INTO users (name, age) VALUES ('Alice', 40);

SELECT * FROM users;
UPDATE users as a SET age = 111 WHERE a.name = 'Alice';
SELECT * FROM users;

修改前表内容如下：

nameage
Alice25
Bob30
Charlie35
Alice40

1 ORACLE

 执行报错

ORA-00971: missing SET keyword

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

2 sqlite

执行正常

后表内容已经更新，如下：

nameage
Alice111
Bob30
Charlie35
Alice111

3 PG

执行正常

后表内容已经更新，如下：

nameage
Bob30
Charlie35
Alice111
Alice111

4 MYSQL & mariadb

执行正常

后表内容已经更新，如下：

nameage
Alice111
Bob30
Charlie35
Alice111

1.4 测试用例UPDATE users as a SET age = 111 WHERE name = 'Alice';

UPDATE users as a SET age = 111 WHERE name = 'Alice';

CREATE TABLE users (
    name VARCHAR(255) NOT NULL,
    age INT
);

INSERT INTO users (name, age) VALUES ('Alice', 25);
INSERT INTO users (name, age) VALUES ('Bob', 30);
INSERT INTO users (name, age) VALUES ('Charlie', 35);
INSERT INTO users (name, age) VALUES ('Alice', 40);

SELECT * FROM users;
UPDATE users as a SET age = 111 WHERE name = 'Alice';
SELECT * FROM users;

修改前表内容如下：

nameage
Alice25
Bob30
Charlie35
Alice40

1 ORACLE

 执行报错

ORA-00971: missing SET keyword

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

2 sqlite

执行正常

后表内容已经更新，如下：

nameage
Alice111
Bob30
Charlie35
Alice111

3 PG

执行正常

后表内容已经更新，如下：

nameage
Bob30
Charlie35
Alice111
Alice111

4 MYSQL & mariadb

执行正常

后表内容已经更新，如下：

nameage
Alice111
Bob30
Charlie35
Alice111

2 delete

2.1 测试用例delete users as a from a WHERE a.name = 'Alice';

delete users as a from a WHERE a.name = 'Alice';

CREATE TABLE users (
    name VARCHAR(255) NOT NULL,
    age INT
);

INSERT INTO users (name, age) VALUES ('Alice', 25);
INSERT INTO users (name, age) VALUES ('Bob', 30);
INSERT INTO users (name, age) VALUES ('Charlie', 35);
INSERT INTO users (name, age) VALUES ('Alice', 40);

SELECT * FROM users;
delete users as a from a WHERE a.name = 'Alice';
SELECT * FROM users;

修改前表内容如下：

nameage
Alice25
Bob30
Charlie35
Alice40

1 ORACLE

 执行报错

ORA-03048: SQL reserved word 'AS' is not syntactically valid following 'delete
users '

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

2 sqlite

 执行报错

Error: near line 12: near "users": syntax error

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

3 PG

 执行报错

psql:commands.sql:12: ERROR:  syntax error at or near "users"
LINE 1: delete users as a from a WHERE a.name = 'Alice';

 之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

4 MYSQL & mariadb

 执行报错

ERROR 1064 (42000) at line 12: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'as a from a WHERE a.name = 'Alice'' at line 1

 之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

2.2 测试用例delete users as a from a WHERE name = 'Alice';

delete users as a from a WHERE name = 'Alice';

CREATE TABLE users (
    name VARCHAR(255) NOT NULL,
    age INT
);

INSERT INTO users (name, age) VALUES ('Alice', 25);
INSERT INTO users (name, age) VALUES ('Bob', 30);
INSERT INTO users (name, age) VALUES ('Charlie', 35);
INSERT INTO users (name, age) VALUES ('Alice', 40);

SELECT * FROM users;
delete users as a from a WHERE name = 'Alice';
SELECT * FROM users;

修改前表内容如下：

nameage
Alice25
Bob30
Charlie35
Alice40

1 ORACLE

 执行报错

ORA-03048: SQL reserved word 'AS' is not syntactically valid following 'delete
users '

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

2 sqlite

 执行报错

Error: near line 12: near "users": syntax error

之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

3 PG

 执行报错

psql:commands.sql:12: ERROR:  syntax error at or near "users"
LINE 1: delete users as a from a WHERE name = 'Alice';

 之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

4 MYSQL & mariadb

 执行报错

ERROR 1064 (42000) at line 12: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'as a from a WHERE name = 'Alice'' at line 1

 之后查询表内容未发生变化，如下：

nameage
Alice25
Bob30
Charlie35
Alice40

总结 

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