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...
16402 | lib2 | 15936 | postgres | active | ::1 | select datid,datname,pid,usename,state,client_addr,query from pg_stat_activity; 16394 | lib1 | 2940 | postgres | idle | 127.0.0.1 | SELECT id,name,age,email FROM guser WHERE id=$1 16402 | lib2 | 18808 | postgres | idle | ...
复制 [root@EULER1~]# su-pg1-c"psql -Upostgres -p 5432 -h 192.168.123.60"Passwordforuser postgres:psql(12.5)Type"help"forhelp.postgres=# create tablespace mytbs location'/opt/custome-tablespace';CREATETABLESPACEpostgres=# \db+Listoftablespaces Name|Owner|Location|Access privileges|Options|Size|...
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 * from emp where ename='SMITH';(字符串类型加单引号) (后面跟集合或者子查询) not in Like %:表示在这个%出现的地方可以有0个或者多个字符 _: 表示在_出现的地方有且只能一个任意字符 --查询emp表中员工姓名第三个字符是A的员工信息
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 ...
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; ...
(1 row) cpu_cost = cpu_tuple_cost * reltuples xiaoming=# select reltuples, current_setting('cpu_tuple_cost') as cpu_tuple_cost, reltuples * current_setting('cpu_tuple_cost')::real AS cpu_cost from pg_class where relname='t1'; reltuples | cpu_tuple_cost | cpu_cost ---+--...
sql = "select match_chunks('[" + ','.join([str(x) for x in embedding]) + "]', 0.78, 5, 50)" cur.execute(sql) rows = cur.fetchall() for row in rows: row = row[0][1:-2].split(',')[-2][1:-2].strip() content = content + row + "\n---\n" ...