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这篇文章主要介绍“PostgreSQL在执行逻辑优化中相关的数据结构是什么”，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是什么问题上存在疑惑，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是什么”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
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FromExpr
表示FROM … WHERE结构
/*----------
* FromExpr - represents a FROM ... WHERE ... construct
* 表示FROM ... WHERE结构
*
* This is both more flexible than a JoinExpr (it can have any number of
* children, including zero) and less so --- we don't need to deal with
* aliases and so on. The output column set is implicitly just the union
* of the outputs of the children.
* 该结构比JoinExpr(有0..n个子节点)更为灵活 -- 不需要处理别名等.
* 输出列集合是子集输出的汇总.
*----------
*/
typedef struct FromExpr
{
NodeTag type;
//连接子树链表
List *fromlist; /* List of join subtrees */
//join中的表达式
Node *quals; /* qualifiers on join, if any */
} FromExpr;JoinExpr
用于SQL JOIN表达式.
/*----------
* JoinExpr - for SQL JOIN expressions
* 用于SQL JOIN表达式.
*
* isNatural, usingClause, and quals are interdependent. The user can write
* only one of NATURAL, USING(), or ON() (this is enforced by the grammar).
* If he writes NATURAL then parse analysis generates the equivalent USING()
* list, and from that fills in "quals" with the right equality comparisons.
* If he writes USING() then "quals" is filled with equality comparisons.
* If he writes ON() then only "quals" is set. Note that NATURAL/USING
* are not equivalent to ON() since they also affect the output column list.
* isNatural, usingClause, and quals是相互依赖的.
* 用户只可以使用NATURAL, USING(), or ON()(语法限制).
* 如果是NATURAL,则解析器会产生相应的USING()链表,并使用正确的等值比较表达式填充quals.
* 如果是USING(),则使用正确的等值比较表达式填充quals.
* 如果是ON(),则只设置quals字段.
* 注意NATURAL/USING与ON()并不相同,因为它们同时影响了输出列链表.
*
* alias is an Alias node representing the AS alias-clause attached to the
* join expression, or NULL if no clause. NB: presence or absence of the
* alias has a critical impact on semantics, because a join with an alias
* restricts visibility of the tables/columns inside it.
* alias表示与join表达式相关的AS别名子句,如无则为NULL.
* 注意:别名的存在与否对语义有很大影响,因此有别名的join限制了其中表/列的可见性.
*
* During parse analysis, an RTE is created for the Join, and its index
* is filled into rtindex. This RTE is present mainly so that Vars can
* be created that refer to the outputs of the join. The planner sometimes
* generates JoinExprs internally; these can have rtindex = 0 if there are
* no join alias variables referencing such joins.
* 在解析时,RTE在参与Join时解析,编号填充到rtindex中.
* 该RTE存在的目的主要是可以创建引用join输出的Vars.
* 计划器有时候会在内部生成JoinExprs;如没有join别名变量参考这样的连接,那么rtindex = 0
*----------
*/
typedef struct JoinExpr
{
NodeTag type;
//join类型
JoinType jointype; /* type of join */
//自然连接?
bool isNatural; /* Natural join? Will need to shape table */
//左树
Node *larg; /* left subtree */
//右树
Node *rarg; /* right subtree */
//USING语句(String链表)
List *usingClause; /* USING clause, if any (list of String) */
//join限定符
Node *quals; /* qualifiers on join, if any */
//别名语句
Alias *alias; /* user-written alias clause, if any */
//分配给join的RT编号,或者为0
int rtindex; /* RT index assigned for join, or 0 */
} JoinExpr;N/A
...
(gdb) p *(FromExpr *)($rte_sq_rte->subquery->jointree)
$44 = {type = T_FromExpr, fromlist = 0x16fda18, quals = 0x16fe0f0}
(gdb) set $rtesq2_jointree=(FromExpr *)($rte_sq_rte->subquery->jointree)
(gdb) p *$rtesq2_jointree->fromlist
$48 = {type = T_List, length = 1, head = 0x16fd9f8, tail = 0x16fd9f8}
(gdb) p *(Node *)$rtesq2_jointree->fromlist->head->data.ptr_value
$49 = {type = T_JoinExpr}
(gdb) set $tmpvar=(JoinExpr *)$rtesq2_jointree->fromlist->head->data.ptr_value
(gdb) p *$tmpvar
$3 = {type = T_JoinExpr, jointype = JOIN_INNER, isNatural = false, larg = 0x2b68730, rarg = 0x2c215e8, usingClause = 0x0, quals = 0x2c28130, alias = 0x0, rtindex = 5}
(gdb) p *$tmpvar->larg
$4 = {type = T_JoinExpr}
(gdb) p *(JoinExpr *)$tmpvar->larg
$5 = {type = T_JoinExpr, jointype = JOIN_INNER, isNatural = false, larg = 0x2c1e848, rarg = 0x2c1ebd8,
usingClause = 0x0, quals = 0x2c20c48, alias = 0x0, rtindex = 3}
(gdb) p *(JoinExpr *)$tmpvar->rarg
$6 = {type = T_RangeTblRef, jointype = JOIN_SEMI, isNatural = 8, larg = 0x2b66de0, rarg = 0x636d7764,
usingClause = 0x10, quals = 0x2b66de0, alias = 0xda, rtindex = 46274048}
(gdb) p *(JoinExpr *)$tmpvar->quals
$7 = {type = T_OpExpr, jointype = 98, isNatural = 67, larg = 0x0, rarg = 0x64, usingClause = 0x2c27fb8,
quals = 0xa9, alias = 0x0, rtindex = 0}
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