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