因此开销计算为 138 次页面读取，每次页面读取将消耗 seq_page_cost (默认1.0)，加上3209*cpu_tuple_cost (默认0.01)即：138*1.0+3209*0.01=170.09现在让我们修改查询并增加一个 WHERE 条件：kfltdb=> EXPLAIN SELECT * FROM t_e_content WHERE contentid < 'CNBJTW2600000005739';QUERY PLAN---Seq ...
23,使用Query Analyzer,查看SQL语句的查询计划和评估分析是否是优化的SQL.一般的20%的代码占据了80%的资源,我们优化的重点是这些慢的地方. 24,如果使用了IN或者OR等时发现查询没有走索引,使用显示申明指定索引: Select * FROM PersonMember (INDEX = IX_Title) Where processid IN ('男','女') 25,将需要查...
58 * variable-length fields start here, but we allow direct access to 59 * proargtypes 60 */61oidvector proargtypes;/* parameter types (excludes OUT params) */6263#ifdefCATALOG_VARLEN64Oid proallargtypes[1];/* all param types (NULL if IN only) */65char proargmodes[1];/* paramete...
数据库集群的逻辑结构 PostgreSQL天然集群,多个集群可以组成集簇,有点类似军队的连、团、旅这样的组织规则。对于我们日常学习使用的单节点则是单个集簇单个集群,自己就是集群。 PostgreSQL如何管理这种集群规则?答案是通过一个无符号4个字节的标识进行管理,一个对象就是集群里的一个数据库。 1.2 数据库对象和对象符号...
[, INTERNALLENGTH = { internal_length | VARIABLE } ] [, PASSEDBYVALUE ] [, ALIGNMENT = alignment ] [, STORAGE = storage ] [, DEFAULT = default ] [, ELEMENT = element ] [, DELIMITER = delimiter ] ) CREATE USER 创建一个新的数据库用户帐户。
] ) CREATE TYPE name ( INPUT = input_function, OUTPUT = output_function [, RECEIVE = receive_function ] [, SEND = send_function ] [, ANALYZE = analyze_function ] [, INTERNALLENGTH = { internal_length | VARIABLE } ] [, PASSEDBYVALUE ] [, ALIGNMENT = alignment ] [, STORAGE = stor...
1 /* parser_init() Initialize to parse one query string */ 2 void parser_init(base_yy_extra_type *yyext) { 3 yyext->parsetree = NIL; /* in case grammar forgets to set it */ 4 } 我们先通过一个标准SELECT语句分析lex和bison输出的scan.c和gram.c代码,从gram.y中给出的SSELECT语句定...
\r reset (clear) the query buffer \s [FILE] display history or save it to file \w FILE write query buffer to file Input/Output \copy ... perform SQL COPY with data stream to the client host \echo [STRING] write string to standard output ...
-- mysqlselectversion()-- 8.3-- 查看配置信息showvariableswherevariable_namein('log_bin','bin...
set psql variable NAME to VALUE (e.g., -v ON_ERROR_STOP=1) -V, --version output version information, then exit -X, --no-psqlrc do not read startup file (~/.psqlrc) -1 ("one"), --single-transaction execute as a single transaction (if non-interactive) ...