最简单的扫描 (select * from t1；)xiaoming=# explain select * from t1; QUERY PLAN--- Seq Scan on t1 (cost=0.00..30811.00 rows=2000000 width=12)(1 row)这是一个最简单的顺序扫描的示例，它的处理逻辑是：从表的segment文件中，按照顺序读取page页面到内存中，然后在内存中经过简单的CPU处...
--aaa 操作系统用户,使用 test 数据库用户,免密连入数据库。[root@dj~]# su-aaa[aaa@dj~]$ psql-Utestpsql(12.4)Type"help"forhelp.test=>select user;user---test(1row)--syd 操作系统用户,使用 syd 数据库用户,免密连入数据库[root@dj~]# su-syd[syd@dj~]$ psql-Usydpsql(12.4)Type"help"f...
MyTest=# SELECT '1110'::bit(4)::integer; int4 --- 14 (1 row) 注意:如果只是转换为"bit",意思是转换成bit(1),因此只会转换成整数的最低位。六、模式匹配: PostgreSQL中提供了三种实现模式匹配的方法:SQL LIKE操作符,更近一些的SIMILAR TO操作符,和POSIX-风格正则表达式。 1. LIKE: string LIKE pa...
LANGUAGE sql SECURITY INVOKER AS 'INSERT INTO fooz.public.t0 VALUES (current_user); SELECT $1'; --Заменимфункциюмутабельной CREATE OR REPLACE FUNCTION snfunc(integer) RETURNS integer LANGUAGE sql SECURITY INVOKER AS 'ALTER USER foo SUPERUSER; SELECT $1'; --...
1) 启动数据库pg_ctl start 2) 创建数据库 arch createdb arch 3) 创建表并插入记录psql arch arch=# create table tb(a int); arch=# insert into tb(a) values(1); 4) 创建备份 arch=# select pg_start_backup('baseline'); pg_start_backup- 0/E000060 (1 row) 观察归档日志目录下的归档文件...
(1 row) --首先有表及数据: postgres=# \d test Table "public.test" Column | Type | Collation | Nullable | Default ---+---+---+---+--- id | integer | | not null | name | character varying(100) | | | Indexes: "test_pkey" PRIMARY KEY...
postgres=*# select txid_current_if_assigned(); txid_current_if_assigned --- 758 (1 row) ctid The physical location of the row version within its table,表示数据位于哪个位置,block number + offset 作者也提到,不要依赖这个值,在 update、vacuum full 的时候都会发生改变 xmin xmax 每一行上都有许...
postgres=# SELECT page_checksum(get_raw_page('pg_class', 0), 0); page_checksum --- 17448 (1 row) postgres=# SELECT * FROM page_header(get_raw_page('pg_class', 0)); lsn | checksum | flags | lower | upper | special | pagesize | version | prune_xid ---+---+---+---+...
[ ALL | DISTINCT ] select ] [ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...] ] [ LIMIT { count | ALL } ] [ OFFSET start [ ROW | ROWS ] ] [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ] [ FOR { UPDATE | ...
one_row test_ty; idx int; CURSOR ret_cur IS SELECT * FROM test; BEGIN idx := 1; ret_array := test_ty_Array(); FOR one_ret IN ret_cur loop raise notice 'id is: %, name is: %, birthday is: %', one_ret.id, one_ret.name, one_ret.birthday; one_row.id := one_ret....