PostgreSQL在执行逻辑优化中相关的数据结构有哪些

这篇文章主要介绍"PostgreSQL在执行逻辑优化中相关的数据结构有哪些"，在日常操作中，相信很多人在PostgreSQL在执行逻辑优化中相关的数据结构有哪些问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答"PostgreSQL在执行逻辑优化中相关的数据结构有哪些"的疑惑有所帮助！接下来，请跟着小编一起来学习吧！

PostgreSQL在执行逻辑优化中相关的数据结构包括RangeSubselect/Alias/RangeVar/ResTarget/ColumnRef.

一、数据结构

RangeSubselect
出现在FROM语句中的子查询

/* * RangeSubselect - subquery appearing in a FROM clause * 出现在FROM语句中的子查询 */typedef struct RangeSubselect{  NodeTag   type;  //是否有LATERAL?  bool    lateral;    /* does it have LATERAL prefix? */  //未转换的子查询语句  Node     *subquery;   /* the untransformed sub-select clause */  //表别名和可选的列别名  Alias    *alias;      /* table alias & optional column aliases */} RangeSubselect;

Alias
为RangeVar指定别名.别名可能同时重命名了表列.

/* * Alias - *    specifies an alias for a range variable; the alias might also *    specify renaming of columns within the table. *    为RangeVar指定别名.别名可能同时重命名了表列. * * Note: colnames is a list of Value nodes (always strings).  In Alias structs * associated with RTEs, there may be entries corresponding to dropped * columns; these are normally empty strings ("").  See parsenodes.h for info. * 注意:colnames是Value节点(通常是字符串)链表. *      在与RTEs相关的Alias结构体中,可能有跟已删除的列对应的条目. *    这些通常是空字符串("").详细可参考parsenodes.h */typedef struct Alias{  NodeTag   type;  //别名  char     *aliasname;    /* aliased rel name (never qualified) */  //列别名链表  List     *colnames;   /* optional list of column aliases */} Alias;

RangeVar
range variable,用于FROM语句中.

/* * RangeVar - range variable, used in FROM clauses * range variable,用于FROM语句中. * * Also used to represent table names in utility statements; there, the alias * field is not used, and inh tells whether to apply the operation * recursively to child tables.  In some contexts it is also useful to carry * a TEMP table indication here. * 在工具语句中,用于表示表名,这时alias字段没有使用. * inh用于判断是否在子表中递归应用相关的操作. */typedef struct RangeVar{  NodeTag   type;  char     *catalogname;  /* the catalog (database) name, or NULL */  char     *schemaname;   /* the schema name, or NULL */  char     *relname;    /* the relation/sequence name */  bool    inh;      /* expand rel by inheritance? recursively act                 * on children? */  char    relpersistence; /* see RELPERSISTENCE_* in pg_class.h */  Alias    *alias;      /* table alias & optional column aliases */  int     location;   /* token location, or -1 if unknown */} RangeVar;

ResTarget
结果目标列(用于先前已转换的解析树的目标链表中)

/* * ResTarget - *    result target (used in target list of pre-transformed parse trees) *    结果目标列(用于先前已转换的解析树的目标链表中) * * In a SELECT target list, 'name' is the column label from an * 'AS ColumnLabel' clause, or NULL if there was none, and 'val' is the * value expression itself.  The 'indirection' field is not used. * 在SELECT的目标链表中, *   'name'是'AS ColumnLabel'语句中的列标签,如无则为NULL, *   'val'是value表达式本身. *   'indirection'未使用. * * INSERT uses ResTarget in its target-column-names list.  Here, 'name' is * the name of the destination column, 'indirection' stores any subscripts * attached to the destination, and 'val' is not used. * INSERT在target-column-names链表中使用ResTarget. * 这里'name'是目标列名称,'indirection'存储了所有与目标相关的子脚本,'val'未使用. * * In an UPDATE target list, 'name' is the name of the destination column, * 'indirection' stores any subscripts attached to the destination, and * 'val' is the expression to assign. * 在UPDATE目标链表中,'name'是目标列名称,'indirection'存储了所有与目标相关的子脚本, * 'val'是与赋值相关的表达式. * * See A_Indirection for more info about what can appear in 'indirection'. * 详细参见A_Indirection('indirection') */typedef struct ResTarget{  NodeTag   type;  //列名或NULL  char     *name;     /* column name or NULL */  //子脚本,字段名称,'*'或NIL  List     *indirection;  /* subscripts, field names, and '*', or NIL */  //需要计算或赋值的值表达式  Node     *val;      /* the value expression to compute or assign */  //token的位置,-1表示未知  int     location;   /* token location, or -1 if unknown */} ResTarget;

ColumnRef
指定对列或整个元组的引用

/* * ColumnRef - specifies a reference to a column, or possibly a whole tuple * 指定对列或整个元组的引用 * * The "fields" list must be nonempty.  It can contain string Value nodes * (representing names) and A_Star nodes (representing occurrence of a '*'). * Currently, A_Star must appear only as the last list element --- the grammar * is responsible for enforcing this! * "fields"链表不能为空.可能包含字符串Value节点和A_Star节点(表示出现了*). * 截止到目前为止,A_Star必须出现在最后一个链表元素中. * * Note: any container subscripting or selection of fields from composite columns * is represented by an A_Indirection node above the ColumnRef.  However, * for simplicity in the normal case, initial field selection from a table * name is represented within ColumnRef and not by adding A_Indirection. */typedef struct ColumnRef{  NodeTag   type;  //字段名称(字符串值)链表或A_Star  List     *fields;     /* field names (Value strings) or A_Star */  //token位置  int     location;   /* token location, or -1 if unknown */} ColumnRef;

二、源码解读

N/A

三、跟踪分析

RangeSubselect/Alias

(gdb) p *(Node *)($stmt->fromClause->head.data->ptr_value)$15 = {type = T_RangeSubselect} #实际类型是范围子查询RangeSubselect(gdb) set $fromclause=(RangeSubselect *)($stmt->fromClause->head.data->ptr_value)(gdb) p *$fromclause$16 = {type = T_RangeSubselect, lateral = false, subquery = 0x1666c18, alias = 0x1666d40}(gdb) p *($fromclause->subquery) #subquery,子查询是SelectStmt类型的节点$17 = {type = T_SelectStmt}(gdb) p *($fromclause->alias) #alias,别名,实际值是字符串ret$18 = {type = T_Alias, aliasname = 0x1666d28 "ret", colnames = 0x0}

RangeVar

...$43 = {type = T_RangeVar}(gdb) p *(RangeVar *)((JoinExpr *)($joinexpr->larg))->larg$44 = {type = T_RangeVar, catalogname = 0x0, schemaname = 0x0, relname = 0x1643380 "t_dwxx", inh = true,   relpersistence = 112 'p', alias = 0x0, location = 82}...

ResTarget

...(gdb) p *(Node *)($subquerylarg->targetList->head.data->ptr_value)$26 = {type = T_ResTarget}(gdb) set $subvar=(ResTarget *)($subquerylarg->targetList->head.data->ptr_value)(gdb) p *$subvar {type = T_ResTarget, name = 0x0, indirection = 0x0, val = 0x1642c70, location = 23}...

ColumnRef

...(gdb) p *$restarget->val$25 = {type = T_ColumnRef}(gdb) p *(ColumnRef *)$restarget->val$26 = {type = T_ColumnRef, fields = 0x1a47a08, location = 7}(gdb) p *((ColumnRef *)$restarget->val)->fields$27 = {type = T_List, length = 2, head = 0x1a47a88, tail = 0x1a479e8}(gdb) p *(Node *)(((ColumnRef *)$restarget->val)->fields)->head.data->ptr_value$32 = {type = T_String}#fields链表的第1个元素是数据表,第2个元素是数据列(gdb) p *(Value *)(((ColumnRef *)$restarget->val)->fields)->head.data->ptr_value$37 = {type = T_String, val = {ival = 27556248, str = 0x1a47998 "t_dwxx"}}(gdb) p *(Value *)(((ColumnRef *)$restarget->val)->fields)->tail.data->ptr_value$38 = {type = T_String, val = {ival = 27556272, str = 0x1a479b0 "dwmc"}}...

到此，关于"PostgreSQL在执行逻辑优化中相关的数据结构有哪些"的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注网站，小编会继续努力为大家带来更多实用的文章！