看下select语句生成的parse tree,query等是什么样的。 CREATE TABLE STUDENT (sno INT primary key, sname VARCHAR(10) not null, ssex varchar(10)); insert into student(sno,sname,ssex) values(1,'zhangsan','male'); insert into student(sno,sname,ssex) values(2,'lisi','male'); insert into ...
SELECT ON test_table TO test_user1; GRANT postgres=# grant select (id),update (name) ON test_table TO test_user1; GRANT postgres=# \dp+ test_table *** QUERY *** SELECT n.nspname as "Schema", c.relname as "Name", CASE c.relkind WHEN 'r' THEN 'table' WHEN 'v' THEN 'view...
CPU: Intel Sandy Bridge microarchitecture, speed 2299.94 MHz (estimated) Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (No unit mask) count 100000 vma samples % linenr info symbol name 00682b07 121678 13.3298 /home/digoal/rds_pg_9400/src/backend/ex...
可以看到内表循环了384次,相当于执行了384次 select ,c.class_name from class where =outer.class_id,每次都是索引扫描,在计算的成本的时候当然该句sql的成本就要乘以384,所以总成本125.88=6.64+384*0.30+联结的成本=122.04+联结的成本。 ②、 postgres=# explain(analyze,verbose,buffers) select s.*,c.class...
pg_replication:query: "SELECT CASE WHEN NOT pg_is_in_recovery() THEN 0 ELSE GREATEST (0, EXTRACT(EPOCH FROM (now() - pg_last_xact_replay_timestamp())) END AS lag"master: truemetrics:- lag:usage: "GAUGE"description: "Replication lag behind master in seconds"pg_postmaster:query: "SELEC...
string NOT LIKE pattern [ ESCAPE escape-character ] 每个pattern定义一个字串的集合。如果该string包含在pattern代表的字串集合里,那么LIKE表达式返回真。和我们想象的一样,如果LIKE返回真,那么NOT LIKE表达式返回假,反之亦然。在pattern里的下划线(_)代表匹配任何单个字符,而一个百分号(%)匹配任何零或更多字符,如...
select * from pg_available_extensions; 初始化一个新的库(安装好了数据库软件): /usr/local/pgsql_100/bin/initdb -D /home/pg_data/pg_data_100 -E UTF-8 --locale=C -U postgres -W CASE WHEN condition_1 THEN result_1 WHEN condition_2 THEN result_2 ...
convert函数不存在 postgreSQL...) mysql可以使用force index强制走索引, postgres没有,建议去掉 2.7、ifnull 函数不存在 postgreSQL没有ifnull函数,用COALESCE函数替换 异常信息...org.postgresql.util.PSQLException: ERROR: function ifnull(numeric, numeric) does not exist 2.8、date_format 函数不存在...内部就...
If there is no index, to_tsvector(foo) should work fine to do a (unindexed) full text search and use the default_text_search_config value. If there is an index, it would not be used to speed up the search though for the same query. If we now change all our queries to by default...
The Postgres EXPLAIN command is invaluable when trying to understand query performance. SQL is a declarative language, and the Postgres query planner will decide the most efficient way to execute a query. However, plan selection is based on statistics, configuration settings, and heuristics—not a ...