话说查询“selectcname,comp from test1,test2 where test1.id=test2.id;” 发送到服务器端，走查询分支exec_simple_query，先调用start_xact_command初始化了事务管理相关对象和资源，接着调用pg_parse_query，通过Lex和Yacc对传入sql语句进行词法语法解析，生成解析树。@H_403_4@

1@H_403_4@

下面是解析sql语句的调用序列图。@H_403_4@

@H_403_4@

@H_403_4@

Postgres服务进程简查之开始事务调用序列图@H_403_4@

@H_403_4@

上图红色方框中显示了解析sql语句的方法调用过程，在raw_parser方法中对sql语句进行词法、语法解析并返回解析树parsetree的列表，因为传入的sql串（从客户端传入）可能有多个命令。@H_403_4@

@H_403_4@

通过Lex和Yacc对传入sql语句进行词法语法解析，主要是把sql语句里的目前字段、DISTINCT子句、FROM子句、WHERE子句、GROUP BY子句、HAVING子句、ORDER BY子句等解析到各自对应的结构中，组织成各自的数据结构，最后组成解析树parsetree。分析完后对应sql语句“selectcname,test2 where test1.id=test2.id;”的解析树结构如下图：@H_403_4@

@H_403_4@

例子中sql语句对应的解析树结构@H_403_4@

pg输出的解析树如下：@H_403_4@

2011-11-2306:57:39 HKT DETAIL: @H_403_4@

{QUERY @H_403_4@

:commandType 1 @H_403_4@

:querySource 0 @H_403_4@

:canSetTag true @H_403_4@

:utilityStmt <> @H_403_4@

:resultRelation 0 @H_403_4@

:intoClause <> @H_403_4@

:hasAggs false @H_403_4@

:hasWindowFuncs false @H_403_4@

:hasSubLinks false @H_403_4@

:hasDistinctOn false @H_403_4@

:hasRecursive false @H_403_4@

:hasModifyingCTE false @H_403_4@

:hasForUpdate false @H_403_4@

:cteList <> @H_403_4@

:rtable (@H_403_4@

{RTE @H_403_4@

:alias <> @H_403_4@

:eref @H_403_4@

{ALIAS @H_403_4@

:aliasname pg_type @H_403_4@

:colnames ("typname" "typnamespace""typowner" "typlen" "typbyval" "t@H_403_4@

yptype" "typcategory" "typispreferred""typisdefined" "typdelim" "typ@H_403_4@

relid" "typelem" "typarray""typinput" "typoutput" "typreceive" "typs@H_403_4@

end" "typmodin" "typmodout""typanalyze" "typalign" "typstorage" "typ@H_403_4@

notnull" "typbasetype" "typtypmod""typndims" "typcollation" "typdefa@H_403_4@

ultbin" "typdefault")@H_403_4@

}@H_403_4@

:rtekind 0 @H_403_4@

:relid 1247 @H_403_4@

:relkind r @H_403_4@

:inh true @H_403_4@

:inFromCl true @H_403_4@

:requiredPerms 2 @H_403_4@

:checkAsUser 0 @H_403_4@

:selectedCols (b 6)@H_403_4@

:modifiedCols (b)@H_403_4@

}@H_403_4@

)@H_403_4@

:jointree @H_403_4@

{FROMEXPR @H_403_4@

:fromlist (@H_403_4@

{RANGETBLREF @H_403_4@

:rtindex 1@H_403_4@

}@H_403_4@

)@H_403_4@

:quals @H_403_4@

{OPEXPR @H_403_4@

:opno 607 @H_403_4@

:opfuncid 184 @H_403_4@

:opresulttype 16 @H_403_4@

:opretset false @H_403_4@

:opcollid 0 @H_403_4@

:inputcollid 0 @H_403_4@

:args (@H_403_4@

{VAR @H_403_4@

:varno 1 @H_403_4@

:varattno -2 @H_403_4@

:vartype 26 @H_403_4@

:vartypmod -1 @H_403_4@

:varcollid 0 @H_403_4@

:varlevelsup 0 @H_403_4@

:varnoold 1 @H_403_4@

:varoattno -2 @H_403_4@

:location 57@H_403_4@

}@H_403_4@

{RELABELTYPE @H_403_4@

:arg @H_403_4@

{CONST @H_403_4@

:consttype 23 @H_403_4@

:consttypmod -1 @H_403_4@

:constcollid 0 @H_403_4@

:constlen 4 @H_403_4@

:constbyval true @H_403_4@

:constisnull false @H_403_4@

:location 63 @H_403_4@

:constvalue 4 [ 19 4 0 0 ]@H_403_4@

}@H_403_4@

:resulttype 26 @H_403_4@

:resulttypmod -1 @H_403_4@

:resultcollid 0 @H_403_4@

:relabelformat 2 @H_403_4@

:location -1@H_403_4@

}@H_403_4@

)@H_403_4@

:location 61@H_403_4@

}@H_403_4@

}@H_403_4@

:targetList (@H_403_4@

{TARGETENTRY @H_403_4@

:expr @H_403_4@

{FUNCEXPR @H_403_4@

:funcid 1081 @H_403_4@

:funcresulttype 25 @H_403_4@

:funcretset false @H_403_4@

:funcformat 0 @H_403_4@

:funccollid 100 @H_403_4@

:inputcollid 0 @H_403_4@

:args (@H_403_4@

{VAR @H_403_4@

:varno 1 @H_403_4@

:varattno -2 @H_403_4@

:vartype 26 @H_403_4@

:vartypmod -1 @H_403_4@

:varcollid 0 @H_403_4@

:varlevelsup 0 @H_403_4@

:varnoold 1 @H_403_4@

:varoattno -2 @H_403_4@

:location 19@H_403_4@

}@H_403_4@

{CONST @H_403_4@

:consttype 23 @H_403_4@

:consttypmod -1 @H_403_4@

:constcollid 0 @H_403_4@

:constlen 4 @H_403_4@

:constbyval true @H_403_4@

:constisnull false @H_403_4@

:location 23 @H_403_4@

:constvalue 4 [ 34 0 0 0 ]@H_403_4@

}@H_403_4@

)@H_403_4@

:location 7@H_403_4@

}@H_403_4@

:resno 1 @H_403_4@

:resname typname @H_403_4@

:ressortgroupref 0 @H_403_4@

:resorigtbl 0 @H_403_4@

:resorigcol 0 @H_403_4@

:resjunk false@H_403_4@

}@H_403_4@

)@H_403_4@

:returningList <> @H_403_4@

:groupClause <> @H_403_4@

:havingQual <> @H_403_4@

:windowClause <> @H_403_4@

:distinctClause <> @H_403_4@

:sortClause <> @H_403_4@

:limitOffset <> @H_403_4@

:limitCount <> @H_403_4@

:rowMarks <> @H_403_4@

:setOperations <> @H_403_4@

:constraintDeps <>@H_403_4@

}@H_403_4@

@H_403_4@

关于进行词法语法分析的Lex和Yacc请参考下面的资料，这些内容引自博客文章《一天之内不再畏惧lex&yacc之必备参考资料》，url是http://blog.sciencenet.cn/blog-419883-309595.html@H_403_4@

1. Lex and YACC primer/HOWTO http://tldp.org/HOWTO/Lex-YACC-HOWTO.html ，短短20页，足够让你建立自信，一个上午足够了吧。@H_403_4@
2. A Compact Guide to Lex & Yacc http://epaperpress.com/lexandyacc/,修行再提高一步，一个下午搞定。@H_403_4@
3. 创始人写的书你得看看吧，Lex and yacc,By John R. Levine,Tony Mason,Doug Brown ，不能下载，没关系，这里有：http://www.filefront.com/16046001/lex--yacc.pdf/ ，第五章Parsing sql你不看一看？晚上吃完饭在教室里摆开架势三个小时敲定这短短30页的第5章，一气呵成，搞定。@H_403_4@

有这三篇文档给你揣在兜里，我想你走路的时候应该“保劲”吧。

@H_403_4@

@H_403_4@

@H_403_4@

@H_403_4@

------------ 转载请注明出处，来自博客： blog.csdn.net/beiigang beigang.iteye.com@H_403_4@