select * from A where exists (select 1 from B where A.id=B.id); 对于以上两种情况,in是在内存里遍历比较,而exists需要查询数据库,所以当B表数据量较大时,exists效率优于in。 1、select * from A where id in (select id from B); in()只执行一次,它查出B表中的所有id字段并缓存起来。之后,检查...
通常用max取出最大值以后,还需要去匹配原表才能拿到原表的其他字段。 用以下两种函数就可以拿原表中任何字段,并且还把最大值带出来了。 1.第一种:where in SELECT * FROM test_table where(name,start_time) in (SELECT name,max(start_time) as start_time FROM test_table GROUP BY name) ; 2.第二...
SELECT tablename FROM pg_tables WHERE tablename NOT LIKE 'pg%' AND tablename NOT LIKE 'sql_%' ORDER BY tablename; 2.列出表中所有的数据 SELECT * FROM someTable; 3.执行外部脚本 #/opt/PostgreSQL/8. 3/bin/psql - Upostgres ;登陆到数据库的控制台界面 postgres= # \i /root/db. sql \i...
* we don't really expect much to be allocated in it. More to the point, * require it to contain at least 8K at all times. This is the only case * where retained memory in a context is *essential* --- we want to be * sure ErrorContext still has some memory even if we've run...
根据输入数组的整数值 intputArr1{1,1,3} inputArr2{13,3,4} * 如果inputArr1[0]==inputArr2...
Query example: select * from mytable where customerId > 1000 and customerId < 2000 or select * from "MyTable". Note in PostgreSQL, the entity name is treated as case-insensitive if not quoted. No String query Schema name If you select Stored procedure as input, specify a schema name ...
在PostgreSQL中,可以使用数组作为WHERE子句中的条件,以实现更灵活的查询。下面是在WHERE子句中使用PostgreSQL数组的方法: 1. 使用ANY关键字:可以使用ANY关键字将数组...
The provider architecture (32-bit or 64-bit) needs to match the architecture of the product where you intent to use the connector. When installing, make sure that you select NpgSQL GAC Installation to ensure NpgSQL itself is added to your machine. The minimun supported PostgreSQL database ...
SELECT col1 FROM tab1 WHERE EXISTS (SELECT 1 FROM tab2 WHERE col2 = tab1.col2); in表达式 expression IN (subquery) row_constructor IN (subquery) not in表达式 expression NOT IN (subquery) row_constructor NOT IN (subquery) any, some表达式(一个意思) expression operator ANY (subquery) ...
sql CREATE INDEX on t(a) WHERE b = 1; as a cache of the query predicate: sql SELECT ... WHERE b = 1 ORDER BY a; This allows the database engine to quickly find rows that use that predicate, as well as (often) retrieve a set of rows in sorted order without having to resort ...