PostgreSQL 源码解读（204）- 查询#117(数据结构SelectStmt&Value)

本节简单介绍了postgresql在执行parse中重要的两个数据结构:SelectStmt&Value.

一、数据结构

SelectStmt
“simple” SELECT可转换为SelectStmt节点.包含集合操作(UNION, INTERSECT, EXCEPT)的查询通过SelectStmt节点树来表示,在这棵树中,叶子节点是SELECTs组件,而内部节点表示UNioN, INTERSECT, or EXCEPT操作符.内部节点和叶子节点是相同的节点类型.

typedef enum SetOperation
{
  SETOP_NONE = 0,
  SETOP_UNION,
  SETOP_INTERSECT,
  SETOP_EXCEPT
} SetOperation;
typedef struct SelectStmt
{
  nodeTag   type;
  
  //NULL,DISTINCT ON表达式链表,或者所有(SELECT DISTINCT)的lcons(NIL,NIL)
  List     *distinctClause; 
  //SELECT INTO的target
  IntoClause *intoClause;   
  //目标链表(元素为ResTarget)
  List     *targetList;   
  //FROM子句
  List     *fromClause;   
  //WHERE
  Node     *whereClause;  
  //GROUP BY 子句
  List     *groupClause;  
  //HAVING条件表达式
  Node     *havingClause; 
  //窗口函数链表
  List     *windowClause; 
  
  List     *valuesLists;  
  
  //排序子句
  List     *sortClause;   
  //limit偏移
  Node     *limitOffset;  
  //limit个数
  Node     *limitCount;   
  //FOR UPDATE
  List     *lockinGClause;  
  //CTE
  WithClause *withClause;   
  
  //操作类型
  SetOperation op;      
  bool    all;      
  //左边树
  struct SelectStmt *larg;  
  //右边树
  struct SelectStmt *rarg;  
  
} SelectStmt;

Value
相同的Value结构体用于5中节点类型:T_Integer, T_Float, T_String, T_BitString, T_Null

#ifndef VALUE_H
#define VALUE_H
#include "nodes/nodes.h"

typedef struct Value
{
  NodeTag   type;     
  union ValUnion
  {
    int     ival;   
    char     *str;    
  }     val;
} Value;
#define intVal(v)   (((Value *)(v))->val.ival)
#define floatVal(v)   atof(((Value *)(v))->val.str)
#define strVal(v)   (((Value *)(v))->val.str)
extern Value *makeInteger(int i);
extern Value *makeFloat(char *numericStr);
extern Value *makeString(char *str);
extern Value *makeBitString(char *str);
#endif              

二、源码解读

N/A

三、跟踪分析

测试sql语句:

-- 用于测试的查询语句
testdb=# select t_dwxx.dwmc,t_grxx.grbh,t_grxx.xm,t_jfxx.ny,t_jfxx.je
testdb-# from t_dwxx,t_grxx,t_jfxx
testdb-# where t_dwxx.dwbh = t_grxx.dwbh 
testdb-# and t_grxx.grbh = t_jfxx.grbh
testdb-# and t_dwxx.dwbh IN ('1001','1002')
testdb-# order by t_grxx.grbh
testdb-# limit 8;
   dwmc    | grbh |  xm  |   ny   |   je   
-----------+------+------+--------+--------
 X有限公司 | 901  | 张三 | 201801 |  401.3
 X有限公司 | 901  | 张三 | 201802 |  401.3
 X有限公司 | 901  | 张三 | 201803 |  401.3
 Y有限公司 | 902  | 李四 | 201801 |  513.1
 Y有限公司 | 902  | 李四 | 201802 |  513.3
 Y有限公司 | 902  | 李四 | 201804 |  513.3
 Y有限公司 | 903  | 王五 | 201801 | 372.22
 Y有限公司 | 903  | 王五 | 201804 | 372.22
(8 rows)

样例数据如下:

...
(gdb) p *(RawStmt *)(raw_parsetree_list->head.data->ptr_value)
$7 = {type = T_RawStmt, stmt = 0x1a48c00, stmt_location = 0, stmt_len = 232}
(gdb) p *((RawStmt *)(raw_parsetree_list->head.data->ptr_value))->stmt
$8 = {type = T_SelectStmt}
###### 实际类型SelectStmt 
(gdb)  p *(SelectStmt *)((RawStmt *)(raw_parsetree_list->head.data->ptr_value))->stmt
$16 = {type = T_SelectStmt, distinctClause = 0x0, intoClause = 0x0, targetList = 0x1a47b18, 
  fromClause = 0x1a48900, whereClause = 0x1a48b40, groupClause = 0x0, havingClause = 0x0, windowClause = 0x0, 
  valuesLists = 0x0, sortClause = 0x1afd858, limitOffset = 0x0, limitCount = 0x1afd888, lockingClause = 0x0, 
  withClause = 0x0, op = SETOP_NONE, all = false, larg = 0x0, rarg = 0x0}

四、参考资料

N/A