Question

我想创建一个类似INSERT IF NOT EXISTS ELSE UPDATE

的SQL查询

我发现Derby能够MERGE，我试图用它来解决我的问题。

MERGE INTO test_table a 
USING test_table b 
ON a.city = 'foo'
WHEN NOT MATCHED THEN INSERT values ( 'foo', '2012-11-11', 'UK')
WHEN MATCHED AND a.modification_date > '1111-11-11' THEN 
      UPDATE SET a.modification_date = '2012-11-11',
                 a.city = 'foo1', 
                 a.country = 'US'

上述声明给出了以下错误：

Error code 30000, SQL state 23505: The statement was aborted because it
would have caused a duplicate key value in a unique or primary key 
constraint or unique index identified by 'SQL150129144920080' defined on 'test_table'

我怎么能运行以下声明：

INSERT INTO test_table values ( 'foo', '2012-11-11', 'UK');

证明上述城市尚未出现在表格中。

我的表包含以下结构：

CREATE TABLE test_table(
       city VARCHAR(100) NOT NULL PRIMARY KEY,
       modification_date DATE NOT NULL,
       country VARCHAR(2) NOT NULL);

非常感谢任何帮助或建议。

Answer 1

您没有将表a连接到表b，因此查询可能会尝试对表B中的每一行执行插入，假设表B包含城市字段，请尝试

MERGE INTO test_table as a
USING test_table b 
ON a.city = b.city and a.city = 'foo'
WHEN NOT MATCHED THEN INSERT values ( 'foo', '2012-11-11', 'UK')
WHEN MATCHED AND a.modification_date > '1111-11-11' THEN 
      UPDATE SET a.modification_date = '2012-11-11',
                 a.city = 'foo1', 
                 a.country = 'US';

Answer 2

您错过了here

中的以下句子

＆＃34;非限定源表名称（或其相关名称）可能与非限定目标表名称（或其相关名称）不同。＆＃34;

这意味着你不能同时使用一个表作为源和目标！

            just one example: 
            we have two schemas: schema1 and schema2 
            and two tables: schema1.table1 and schema2.table1 
            --i have to write all details: 
            create schema schema1; 
            create table schema1.table1 (
              name varchar(255) not null, 
              id int not null primary key 
            ); 

            create schema schema2; 
            create table schema2.table1 (
                name varchar(255) not null, 
              id int not null primary key 
            ); 


            --suppose we have inserted  some entries into schema2.table1 
            insert into schema2.table1 values 
            ('foo', 1), ('bar', 2); 

            --and we want just to copy values from schema2.table1 into schema1.table1 
            --apply MERGE INTO ... INSERT ... 
            merge into schema1.table1 as tableTarget 
            using schema2.table1 as tableSrc 
            on tableTarget.id= tableSrc.id 
            when matched then 
             update set tableTarget.name=tableSrc.name 
             when not matched then 
              insert(name, id) values (tableSrc.name, tableSrc.id); 

              --that has to work

Derby Merge插入不起作用

2 个答案: