UPDATEbus_historyT1,(SELECTT2.id,T2.user_accounts,GROUP_CONCAT(T4.user_name)ASuser_namesFROMbus_historyT2JOINmysql.help_topicT3ONT3.help_topic_id<(LENGTH(T1.user_accounts)-LENGTH(REPLACE(T1.user_accounts,',','')
In this tutorial, we will learn about the UPDATE JOIN statement. The UPDATE JOIN statement is basically used to update the table data based on the joins. We will see how to perform the update join operation using the left join as well as the inner join. So, let’s get started! Also ...
对于select语句,我们可以通过join/outer join来关联多个表;但是对于update语句,是不能直接通过join/outer join来关联多表数据的,这里仅针对PostgreSQL。 或者说,在PostgreSQL中,就算使用update+join不会报错,但join的那部分其实是没任何效果的,如下所示: 1 2 3 4 5 6 7 8 update a set value = 'test' from ...
SELECT'update table_update set field='''||update_field||''',ts=to_char(sysdate,''yyyy-mm-dd hh24:mi:ss'') where key_field='''||query_field||''';'from(selectquery_field_key,update_fieldfromtable1 t1innerjointable2 t2ont1.field=t2.field ) 方式3: merge into mergeinto<update_ta...
熟悉oracle 的人都知道,对于两表的关联更新,其执行计划主要有 Filter 和 Outer Join 两种方式。对于大批量数据的update,Join方式明显是更优的选择。KingbaseES 和 Postgresql 也支持两种方式的关联update,语法上采用两种不同的写法。 以下以例子的形式展示两种写法及性能上的差异。这些例子同时通过KingbaseES V8R6和 ...
create table testb as select * from dba_objects where rownum<=30000; --数据源表关联字段上要有索引, 可以先不建, 看看效率 create unique index UIDX_TESTA_OBJECT_ID on testa(object_id); 1. 2. 3. 4. 5. 6. 7. 8. 二、 各种关联update写法 ...
EXPLAIN SELECT * FROM class LEFT JOIN book ON class.card = book.card; 1. 2. 可以看到,在从表上建立索引之后,需要搜索的行数明显减少。 原因在于,外连接时,主表的信息本来就要全部出现在结果之中,所以在主表上建立索引的效果差于在从表上建立索引的效果。
JOIN| |1 |93 | |2 | SORT | |2 |47 | |3 | TABLE SCAN |T1 |2 |46 | |4 | SORT | |1 |46 | |5 | TABLE SCAN |T2 |1 |46 | === Outputs & filters: --- 0 - output(nil), filter(nil), columns([{TEST1: ({TEST1: (T1.__pk_increment, T1.A, T1.B)})}]), parti...
This is why the UPDATE LEFT JOIN comes to the rescue. The UPDATE LEFT JOIN statement basically updates a record in a table when it does not have a corresponding record in another table. For example, you can increase the salary for a new hire by 1.5% using the following statement: UPDATE...
The condition is defined by a join operation between the "bill" table and the "patient" table, based on the equality of the "patient_id" column in both tables. The join is performed using the "INNER JOIN" keyword, which returns only the rows from both tables where there is a match be...