分析器会先看语句的第一个词,当它发现第一个词是SELECT关键字的时候,它会跳到FROM关键字,然后通过FROM关键字找到表名并把表装入内存。接着是找WHERE关键字,如果找不到则返回到SELECT找字段解析,如果找到WHERE,则分析其中的条件,完成后再回到SELECT分析字段。最后形成一张我们要的虚表。 WHERE关键字后面的是条件表...
CREATETABLEfoo (fooidint, foosubidint, fooname text);CREATEFUNCTIONgetfoo(int)RETURNSSETOF fooAS$$SELECT*FROMfooWHEREfooid=$1; $$LANGUAGESQL;SELECT*FROMgetfoo(1)ASt1;SELECT*FROMfooWHEREfoosubidIN(SELECTfoosubidFROMgetfoo(foo.fooid) zWHEREz.fooid=foo.fooid );CREATEVIEWvw_getfooASSELECT...
postgres=# explain select * from customers where status = 'EXPIRED1' and arr > 30; QUERY PLAN --- Seq Scan on cust_archived customers (cost=0.00..22.75 rows=1 width=68) Filter: ((arr > '30'::numeric) AND (status = 'EXPIRED1'::text)) 不带分区键查询:不知道数据在哪个子表,全部扫...
select 列名,列名,..,列名 from 表名 where 条件表达式 order by 排序列的列名(后可跟多个列,按照紧跟order by关键字的列排序,如果第一个排序字段的值相同,再按照第二个排序) asc(升序可省略)|desc(降序); 注意:order by 后面除了可以跟表中的列名外,还可以跟select 和from之间查询结果的序号 select empno,...
SELECT pg_size_pretty (pg_tablespace_size ('tablespace_name')); 8. 获取 Postgres 中所有数据库的列表及其大小(以 GB 为单位),按最大大小排序 SELECT pg_database.datnameas"database_name", pg_database_size(pg_database.datname)/1024/1024/1024AS size_in_GB FROM pg_database ORDER by size_...
"void" AS $BODY$ DECLARE obj record; BEGIN FOR obj IN (SELECT n.nspname, c.relname, c.relhaspkey FROM pg_catalog.pg_class c LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace WHERE c.relkind = 'r' AND n.nspname <> 'pg_catalog' AND n.nspname <> 'information...
那如果按照有些回答那样,先建一个临时表,然后用in subquery,并且希望这时候可以两表join呢?为了简单我直接用两表join了 droptablet_tmp;createtablet_tmp(idint);insertintot_tmp (id)values(494613),(575087),(363588),(345980),...(1);selectt9.*fromt9, t_tmpwhere t9.c1 = t_tmp.id; ...
ALTER DEFAULT PRIVILEGES [ FOR { ROLE | USER } target_role [, ...] ] [ IN SCHEMA schema_name [, ...] ] abbreviated_grant_or_revoke where abbreviated_grant_or_revoke is one of: GRANT { { SELECT | INSERT | UPDATE | DELETE | TRUNCATE | REFERENCES | TRIGGER } [, ...] | ALL ...
查看表d的第一个 page 的tuple信息SELECT * FROM heap_page_items(get_raw_page('d', 0));,其中heap_page_items获取 page 内部每一个heaptuple元组条目信息:shell testdb=# SELECT * FROM heap_page_items(get_raw_page('d', 0)) where lp < 5; lp | lp_off | lp_flags | lp_len | t_xmi...
T2 # select * from tym_account where account_no = 1; # select * from tym_account where account_no = 2; T3 # update tym_account set account_name = 'TYM22' where account_no = 2; # update tym_account set account_name = 'TYM11' where account_no = 1; T4 # commit; T5 # comm...