PostgreSQL 原始碼解讀（20）- 查詢語句#5（查詢樹Query詳解）
本文簡單介紹了PG查詢優化重寫後生成的查詢樹Query的詳細結構，查詢重寫優化的輸入是上一節介紹的解析樹Parsetree。
一、查詢樹結構
查詢語句：
testdb=# select * from (
testdb(# select t_dwxx.dwmc,t_grxx.grbh,t_grxx.xm,t_jfxx.ny,t_jfxx.je
testdb(# from t_dwxx inner join t_grxx on t_dwxx.dwbh = t_grxx.dwbh
testdb(# inner join t_jfxx on t_grxx.grbh = t_jfxx.grbh
testdb(# where t_dwxx.dwbh IN ('1001')
testdb(# union all
testdb(# select t_dwxx.dwmc,t_grxx.grbh,t_grxx.xm,t_jfxx.ny,t_jfxx.je
testdb(# from t_dwxx inner join t_grxx on t_dwxx.dwbh = t_grxx.dwbh
testdb(# inner join t_jfxx on t_grxx.grbh = t_jfxx.grbh
testdb(# where t_dwxx.dwbh IN ('1002')
testdb(# ) as ret
testdb-# order by ret.grbh
testdb-# limit 4;
跟蹤分析：
(gdb) b exec_simple_query
Breakpoint 1 at 0x84cad8: file postgres.c, line 893.
(gdb) c
Continuing.
1047 querytree_list = pg_analyze_and_rewrite(parsetree, query_string,
(gdb)
1050 plantree_list = pg_plan_queries(querytree_list,
(gdb) p *querytree_list
$1 = {type = T_List, length = 1, head = 0x170c858, tail = 0x170c858}
(gdb) p *(Node *)(querytree_list->head->data.ptr_value)
$2 = {type = T_Query}
(gdb) p *(Query *)(querytree_list->head->data.ptr_value)
$3 = {type = T_Query, commandType = CMD_SELECT, querySource = QSRC_ORIGINAL, queryId = 0, canSetTag = true,
utilityStmt = 0x0, resultRelation = 0, hasAggs = false, hasWindowFuncs = false, hasTargetSRFs = false,
hasSubLinks = false, hasDistinctOn = false, hasRecursive = false, hasModifyingCTE = false,
hasForUpdate = false, hasRowSecurity = false, cteList = 0x0, rtable = 0x170be68, jointree = 0x170c7d8,
targetList = 0x170c428, override = OVERRIDING_NOT_SET, onConflict = 0x0, returningList = 0x0,
groupClause = 0x0, groupingSets = 0x0, havingQual = 0x0, windowClause = 0x0, distinctClause = 0x0,
sortClause = 0x170c6b8, limitOffset = 0x0, limitCount = 0x170c788, rowMarks = 0x0, setOperations = 0x0,
constraintDeps = 0x0, withCheckOptions = 0x0, stmt_location = 0, stmt_len = 455}
(gdb) set $query=(Query *)(querytree_list->head->data.ptr_value)
Query->rtable
#---------------------->rtable
(gdb) set $rtable=$query->rtable
(gdb) p *$rtable
$8 = {type = T_List, length = 3, head = 0x170be48, tail = 0x170f6b0}
(gdb) p *(Node *)($rtable->head->data.ptr_value)
$9 = {type = T_RangeTblEntry}
(gdb) p *(RangeTblEntry *)($rtable->head->data.ptr_value)
$10 = {type = T_RangeTblEntry, rtekind = RTE_SUBQUERY, relid = 0, relkind = 0 '\000', tablesample = 0x0,
subquery = 0x1667500, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0,
functions = 0x0, funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0,
ctelevelsup = 0, self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0,
enrname = 0x0, enrtuples = 0, alias = 0x1666d40, eref = 0x170bc18, lateral = false, inh = true,
inFromCl = true, requiredPerms = 2, checkAsUser = 0, selectedCols = 0x0, insertedCols = 0x0,
updatedCols = 0x0, securityQuals = 0x0}
(gdb) set $rte=(RangeTblEntry *)($rtable->head->data.ptr_value)
(gdb) p *$rte->subquery
$12 = {type = T_Query, commandType = CMD_SELECT, querySource = QSRC_ORIGINAL, queryId = 0, canSetTag = true,
utilityStmt = 0x0, resultRelation = 0, hasAggs = false, hasWindowFuncs = false, hasTargetSRFs = false,
hasSubLinks = false, hasDistinctOn = false, hasRecursive = false, hasModifyingCTE = false,
hasForUpdate = false, hasRowSecurity = false, cteList = 0x0, rtable = 0x16fe4e8, jointree = 0x170bbe8,
targetList = 0x170b358, override = OVERRIDING_NOT_SET, onConflict = 0x0, returningList = 0x0,
groupClause = 0x0, groupingSets = 0x0, havingQual = 0x0, windowClause = 0x0, distinctClause = 0x0,
sortClause = 0x0, limitOffset = 0x0, limitCount = 0x0, rowMarks = 0x0, setOperations = 0x1667610,
constraintDeps = 0x0, withCheckOptions = 0x0, stmt_location = 0, stmt_len = 0}
(gdb) p *$rte->alias
$13 = {type = T_Alias, aliasname = 0x1666d28 "ret", colnames = 0x0}
(gdb) p *$rte->eref
$14 = {type = T_Alias, aliasname = 0x170bc48 "ret", colnames = 0x170bcb8}
(gdb) p *$rte->eref->colnames
$15 = {type = T_List, length = 5, head = 0x170bc98, tail = 0x170be28}
(gdb) p *(Node *)$rte->eref->colnames->head->data.ptr_value
$16 = {type = T_String}
(gdb) p *(Value *)$rte->eref->colnames->head->data.ptr_value
$17 = {type = T_String, val = {ival = 24165472, str = 0x170bc60 "dwmc"}}
---->subquery
(gdb) p *(RangeTblEntry *)$rte->subquery->rtable->head->data.ptr_value
$26 = {type = T_RangeTblEntry, rtekind = RTE_SUBQUERY, relid = 0, relkind = 0 '\000', tablesample = 0x0,
subquery = 0x16faf98, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0,
functions = 0x0, funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0,
ctelevelsup = 0, self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0,
enrname = 0x0, enrtuples = 0, alias = 0x16fe240, eref = 0x16fe290, lateral = false, inh = false,
inFromCl = false, requiredPerms = 0, checkAsUser = 0, selectedCols = 0x0, insertedCols = 0x0,
updatedCols = 0x0, securityQuals = 0x0}
(gdb) set $rte_sq_rte=((RangeTblEntry *)$rte->subquery->rtable->head->data.ptr_value)
(gdb) p *(RangeTblEntry *)$rte_sq_rte->subquery->rtable->head->data.ptr_value
$30 = {type = T_RangeTblEntry, rtekind = RTE_RELATION, relid = 26754, relkind = 114 'r', tablesample = 0x0,
subquery = 0x0, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0, functions = 0x0,
funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0, ctelevelsup = 0,
self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0, enrname = 0x0,
enrtuples = 0, alias = 0x0, eref = 0x16677c0, lateral = false, inh = true, inFromCl = true,
requiredPerms = 2, checkAsUser = 0, selectedCols = 0x16fbda8, insertedCols = 0x0, updatedCols = 0x0,
securityQuals = 0x0}
(gdb) set $rte_sq_rte_sq_rte=(RangeTblEntry *)$rte_sq_rte->subquery->rtable->head->data.ptr_value
(gdb) p *$rte_sq_rte_sq_rte
$42 = {type = T_RangeTblEntry, rtekind = RTE_RELATION, relid = 26754, relkind = 114 'r', tablesample = 0x0,
subquery = 0x0, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0, functions = 0x0,
funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0, ctelevelsup = 0,
self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0, enrname = 0x0,
enrtuples = 0, alias = 0x0, eref = 0x16677c0, lateral = false, inh = true, inFromCl = true,
requiredPerms = 2, checkAsUser = 0, selectedCols = 0x16fbda8, insertedCols = 0x0, updatedCols = 0x0,
securityQuals = 0x0}
(gdb) set $rte_sq_rte_sq_rtable=$rte_sq_rte->subquery->rtable
(gdb) p *(RangeTblEntry *)($rte_sq_rte_sq_rtable->head->data.ptr_value)
$60 = {type = T_RangeTblEntry, rtekind = RTE_RELATION, relid = 26754, relkind = 114 'r', tablesample = 0x0,
subquery = 0x0, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0, functions = 0x0,
funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0, ctelevelsup = 0,
self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0, enrname = 0x0,
enrtuples = 0, alias = 0x0, eref = 0x16677c0, lateral = false, inh = true, inFromCl = true,
requiredPerms = 2, checkAsUser = 0, selectedCols = 0x16fbda8, insertedCols = 0x0, updatedCols = 0x0,
securityQuals = 0x0}
(gdb) p *(RangeTblEntry *)($rte_sq_rte_sq_rtable->head->next->data.ptr_value)
$61 = {type = T_RangeTblEntry, rtekind = RTE_RELATION, relid = 26757, relkind = 114 'r', tablesample = 0x0,
subquery = 0x0, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0, functions = 0x0,
funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0, ctelevelsup = 0,
self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0, enrname = 0x0,
enrtuples = 0, alias = 0x0, eref = 0x16fb4f0, lateral = false, inh = true, inFromCl = true,
requiredPerms = 2, checkAsUser = 0, selectedCols = 0x16fbe10, insertedCols = 0x0, updatedCols = 0x0,
securityQuals = 0x0}
(gdb) p *(RangeTblEntry *)($rte_sq_rte_sq_rtable->head->next->next->data.ptr_value)
$62 = {type = T_RangeTblEntry, rtekind = RTE_JOIN, relid = 0, relkind = 0 '\000', tablesample = 0x0,
subquery = 0x0, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x16fbff8,
functions = 0x0, funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0,
ctelevelsup = 0, self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0,
enrname = 0x0, enrtuples = 0, alias = 0x0, eref = 0x16fc318, lateral = false, inh = false, inFromCl = true,
requiredPerms = 0, checkAsUser = 0, selectedCols = 0x0, insertedCols = 0x0, updatedCols = 0x0,
securityQuals = 0x0}
(gdb) p *(RangeTblEntry *)($rte_sq_rte_sq_rtable->head->next->next->next->data.ptr_value)
$63 = {type = T_RangeTblEntry, rtekind = RTE_RELATION, relid = 26760, relkind = 114 'r', tablesample = 0x0,
subquery = 0x0, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0, functions = 0x0,
funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0, ctelevelsup = 0,
self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0, enrname = 0x0,
enrtuples = 0, alias = 0x0, eref = 0x16fc678, lateral = false, inh = true, inFromCl = true,
requiredPerms = 2, checkAsUser = 0, selectedCols = 0x16fd1d0, insertedCols = 0x0, updatedCols = 0x0,
securityQuals = 0x0}
(gdb) p *(RangeTblEntry *)($rte_sq_rte_sq_rtable->tail->data.ptr_value)
$64 = {type = T_RangeTblEntry, rtekind = RTE_JOIN, relid = 0, relkind = 0 '\000', tablesample = 0x0,
subquery = 0x0, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x16fd3b8,
functions = 0x0, funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0,
ctelevelsup = 0, self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0,
enrname = 0x0, enrtuples = 0, alias = 0x0, eref = 0x16fd798, lateral = false, inh = false, inFromCl = true,
requiredPerms = 0, checkAsUser = 0, selectedCols = 0x0, insertedCols = 0x0, updatedCols = 0x0,
securityQuals = 0x0}
(gdb) p *(FromExpr *)($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
$7 = {type = T_OpExpr, jointype = 98, isNatural = 67, larg = 0x0, rarg = 0x64, usingClause = 0x2c27fb8,
quals = 0xa9, alias = 0x0, rtindex = 0}
(gdb) p *((JoinExpr *)$tmpvar->larg)->larg
$8 = {type = T_RangeTblRef}
(gdb) p *(RangeTblRef *)((JoinExpr *)$tmpvar->larg)->larg
$9 = {type = T_RangeTblRef, rtindex = 1}
(gdb) p *(RangeTblRef *)((JoinExpr *)$tmpvar->larg)->rarg
$10 = {type = T_RangeTblRef, rtindex = 2}
(gdb) p *(RangeTblRef *)((JoinExpr *)$tmpvar->larg)->quals
$11 = {type = T_OpExpr, rtindex = 98}
(gdb) p *(Node *)((JoinExpr *)$tmpvar->larg)->quals
$12 = {type = T_OpExpr}
(gdb) p *(OpExpr *)((JoinExpr *)$tmpvar->larg)->quals
$13 = {xpr = {type = T_OpExpr}, opno = 98, opfuncid = 67, opresulttype = 16, opretset = false, opcollid = 0,
inputcollid = 100, args = 0x2c20b88, location = 122}
(gdb) p *((OpExpr *)((JoinExpr *)$tmpvar->larg)->quals)->args
$72 = {type = T_List, length = 2, head = 0x2c20bd8, tail = 0x2c20bb8}
(gdb) p *(Node *)((OpExpr *)((JoinExpr *)$tmpvar->larg)->quals)->args->head->data.ptr_value
$73 = {type = T_RelabelType}
(gdb) p *(RelabelType *)((OpExpr *)((JoinExpr *)$tmpvar->larg)->quals)->args->head->data.ptr_value
$74 = {xpr = {type = T_RelabelType}, arg = 0x2c1f1d8, resulttype = 25, resulttypmod = -1, resultcollid = 100,
relabelformat = COERCE_IMPLICIT_CAST, location = -1}
(gdb) p *((RelabelType *)((OpExpr *)((JoinExpr *)$tmpvar->larg)->quals)->args->head->data.ptr_value))->arg
Junk after end of expression.
(gdb) p *((RelabelType *)((OpExpr *)((JoinExpr *)$tmpvar->larg)->quals)->args->head->data.ptr_value)->arg
$75 = {type = T_Var}
(gdb) p *(Var *)((RelabelType *)((OpExpr *)((JoinExpr *)$tmpvar->larg)->quals)->args->head->data.ptr_value)->arg
$76 = {xpr = {type = T_Var}, varno = 1, varattno = 2, vartype = 1043, vartypmod = 14, varcollid = 100,
varlevelsup = 0, varnoold = 1, varoattno = 2, location = 110}
(gdb) p *(Var *)((RelabelType *)((OpExpr *)((JoinExpr *)$tmpvar->larg)->quals)->args->tail->data.ptr_value)->arg
$77 = {xpr = {type = T_Var}, varno = 2, varattno = 1, vartype = 1043, vartypmod = 14, varcollid = 100,
varlevelsup = 0, varnoold = 2, varoattno = 1, location = 124}
(gdb) p *(RangeTblRef *)((JoinExpr *)$tmpvar)->rarg
$24 = {type = T_RangeTblRef, rtindex = 4}
(gdb) set $rtesq2_targetList=($rte_sq_rte->subquery->targetList)
(gdb) p *$rtesq2_targetList
$30 = {type = T_List, length = 5, head = 0x2c28840, tail = 0x2c28b70}
(gdb) p *(Node *)$rtesq2_targetList->head->data.ptr_value
$32 = {type = T_TargetEntry}
(gdb) p *(TargetEntry *)$rtesq2_targetList->head->data.ptr_value
$33 = {xpr = {type = T_TargetEntry}, expr = 0x2c28770, resno = 1, resname = 0x2b67be8 "dwmc",
ressortgroupref = 0, resorigtbl = 26754, resorigcol = 1, resjunk = false}
(gdb) p *$rte->subquery->rtable
$34 = {type = T_List, length = 2, head = 0x2c2a200, tail = 0x2c2d5f8}
(gdb) set $rte_sq_rte2=((RangeTblEntry *)$rte->subquery->rtable->head->next->data.ptr_value)
#分析過程類似於rte1
(gdb) p *$rte_sq_rte2
$35 = {type = T_RangeTblEntry, rtekind = RTE_SUBQUERY, relid = 0, relkind = 0 '\000', tablesample = 0x0,
subquery = 0x2c211b8, security_barrier = false, jointype = JOIN_INNER, joinaliasvars = 0x0,
functions = 0x0, funcordinality = false, tablefunc = 0x0, values_lists = 0x0, ctename = 0x0,
ctelevelsup = 0, self_reference = false, coltypes = 0x0, coltypmods = 0x0, colcollations = 0x0,
enrname = 0x0, enrtuples = 0, alias = 0x2c2d370, eref = 0x2c2d3c0, lateral = false, inh = false,
inFromCl = false, requiredPerms = 0, checkAsUser = 0, selectedCols = 0x0, insertedCols = 0x0,
updatedCols = 0x0, securityQuals = 0x0}
(gdb)
(gdb) p *(FromExpr *)$rte->subquery->jointree
$41 = {type = T_FromExpr, fromlist = 0x0, quals = 0x0}
(gdb) p *$rte->subquery->targetList
$45 = {type = T_List, length = 5, head = 0x2c2ddb8, tail = 0x2c2e328}
(gdb) p *(Node *)$rte->subquery->targetList->head->data.ptr_value
$46 = {type = T_TargetEntry}
(gdb) p *(TargetEntry *)$rte->subquery->targetList->head->data.ptr_value
$47 = {xpr = {type = T_TargetEntry}, expr = 0x2c2dd18, resno = 1, resname = 0x2c2dd00 "dwmc",
ressortgroupref = 0, resorigtbl = 0, resorigcol = 0, resjunk = false}
Query->jointree
#---------------------->jointree
(gdb) p *$query->jointree
$50 = {type = T_FromExpr, fromlist = 0x2c2e9c0, quals = 0x0}
(gdb) p *$query->jointree->fromlist
$51 = {type = T_List, length = 1, head = 0x2c2e9a0, tail = 0x2c2e9a0}
(gdb) p *(Node *)$query->jointree->fromlist->head->data.ptr_value
$52 = {type = T_RangeTblRef}
(gdb)
Query->targetList
#---------------------->targetList
(gdb) p *$query->targetList
$54 = {type = T_List, length = 5, head = 0x2c2ee88, tail = 0x2c2f078}
(gdb) p *(TargetEntry *)$query->targetList->head->data.ptr_value
$55 = {xpr = {type = T_TargetEntry}, expr = 0x2c2ea78, resno = 1, resname = 0x2c2e9f0 "dwmc",
ressortgroupref = 0, resorigtbl = 0, resorigcol = 0, resjunk = false}
(gdb)
(gdb)
Query->sortClause
#---------------------->sortClause
(gdb) p *(Node *)$query->sortClause->head->data.ptr_value
$57 = {type = T_SortGroupClause}
(gdb) p *(SortGroupClause *)$query->sortClause->head->data.ptr_value
$58 = {type = T_SortGroupClause, tleSortGroupRef = 1, eqop = 98, sortop = 664, nulls_first = false,
hashable = true}
Query->limitCount
#---------------------->limitCount
(gdb) p *$query->limitCount
$59 = {type = T_FuncExpr}
(gdb) p *(FuncExpr *)$query->limitCount
$60 = {xpr = {type = T_FuncExpr}, funcid = 481, funcresulttype = 20, funcretset = false,
funcvariadic = false, funcformat = COERCE_IMPLICIT_CAST, funccollid = 0, inputcollid = 0, args = 0x2c2fa68,
location = -1}
(gdb)
SQL語句最終的查詢樹結構如下:
查詢樹
注意：RangeTblRef中的rtindex指向的是rtable連結串列RangeTblEntry的Index。
二、資料結構
RangeTblEntry
/*--------------------
* RangeTblEntry -
* A range table is a List of RangeTblEntry nodes.
*
* A range table entry may represent a plain relation, a sub-select in
* FROM, or the result of a JOIN clause. (Only explicit JOIN syntax
* produces an RTE, not the implicit join resulting from multiple FROM
* items. This is because we only need the RTE to deal with SQL features
* like outer joins and join-output-column aliasing.) Other special
* RTE types also exist, as indicated by RTEKind.
*
* Note that we consider RTE_RELATION to cover anything that has a pg_class
* entry. relkind distinguishes the sub-cases.
*
* alias is an Alias node representing the AS alias-clause attached to the
* FROM expression, or NULL if no clause.
*
* eref is the table reference name and column reference names (either
* real or aliases). Note that system columns (OID etc) are not included
* in the column list.
* eref->aliasname is required to be present, and should generally be used
* to identify the RTE for error messages etc.
*
* In RELATION RTEs, the colnames in both alias and eref are indexed by
* physical attribute number; this means there must be colname entries for
* dropped columns. When building an RTE we insert empty strings ("") for
* dropped columns. Note however that a stored rule may have nonempty
* colnames for columns dropped since the rule was created (and for that
* matter the colnames might be out of date due to column renamings).
* The same comments apply to FUNCTION RTEs when a function's return type
* is a named composite type.
*
* In JOIN RTEs, the colnames in both alias and eref are one-to-one with
* joinaliasvars entries. A JOIN RTE will omit columns of its inputs when
* those columns are known to be dropped at parse time. Again, however,
* a stored rule might contain entries for columns dropped since the rule
* was created. (This is only possible for columns not actually referenced
* in the rule.) When loading a stored rule, we replace the joinaliasvars
* items for any such columns with null pointers. (We can't simply delete
* them from the joinaliasvars list, because that would affect the attnums
* of Vars referencing the rest of the list.)
*
* inh is true for relation references that should be expanded to include
* inheritance children, if the rel has any. This *must* be false for
* RTEs other than RTE_RELATION entries.
*
* inFromCl marks those range variables that are listed in the FROM clause.
* It's false for RTEs that are added to a query behind the scenes, such
* as the NEW and OLD variables for a rule, or the subqueries of a UNION.
* This flag is not used anymore during parsing, since the parser now uses
* a separate "namespace" data structure to control visibility, but it is
* needed by ruleutils.c to determine whether RTEs should be shown in
* decompiled queries.
*
* requiredPerms and checkAsUser specify run-time access permissions
* checks to be performed at query startup. The user must have *all*
* of the permissions that are OR'd together in requiredPerms (zero
* indicates no permissions checking). If checkAsUser is not zero,
* then do the permissions checks using the access rights of that user,
* not the current effective user ID. (This allows rules to act as
* setuid gateways.) Permissions checks only apply to RELATION RTEs.
*
* For SELECT/INSERT/UPDATE permissions, if the user doesn't have
* table-wide permissions then it is sufficient to have the permissions
* on all columns identified in selectedCols (for SELECT) and/or
* insertedCols and/or updatedCols (INSERT with ON CONFLICT DO UPDATE may
* have all 3). selectedCols, insertedCols and updatedCols are bitmapsets,
* which cannot have negative integer members, so we subtract
* FirstLowInvalidHeapAttributeNumber from column numbers before storing
* them in these fields. A whole-row Var reference is represented by
* setting the bit for InvalidAttrNumber.
*
* securityQuals is a list of security barrier quals (boolean expressions),
* to be tested in the listed order before returning a row from the
* relation. It is always NIL in parser output. Entries are added by the
* rewriter to implement security-barrier views and/or row-level security.
* Note that the planner turns each boolean expression into an implicitly
* AND'ed sublist, as is its usual habit with qualification expressions.
*--------------------
*/
typedef enum RTEKind
{
RTE_RELATION, /* ordinary relation reference */
RTE_SUBQUERY, /* subquery in FROM */
RTE_JOIN, /* join */
RTE_FUNCTION, /* function in FROM */
RTE_TABLEFUNC, /* TableFunc(.., column list) */
RTE_VALUES, /* VALUES (<exprlist>), (<exprlist>), ... */
RTE_CTE, /* common table expr (WITH list element) */
RTE_NAMEDTUPLESTORE /* tuplestore, e.g. for AFTER triggers */
} RTEKind;
typedef struct RangeTblEntry
{
NodeTag type;
RTEKind rtekind; /* see above */
/*
* XXX the fields applicable to only some rte kinds should be merged into
* a union. I didn't do this yet because the diffs would impact a lot of
* code that is being actively worked on. FIXME someday.
*/
/*
* Fields valid for a plain relation RTE (else zero):
*
* As a special case, RTE_NAMEDTUPLESTORE can also set relid to indicate
* that the tuple format of the tuplestore is the same as the referenced
* relation. This allows plans referencing AFTER trigger transition
* tables to be invalidated if the underlying table is altered.
*/
Oid relid; /* OID of the relation */
char relkind; /* relation kind (see pg_class.relkind) */
struct TableSampleClause *tablesample; /* sampling info, or NULL */
/*
* Fields valid for a subquery RTE (else NULL):
*/
Query *subquery; /* the sub-query */
bool security_barrier; /* is from security_barrier view? */
/*
* Fields valid for a join RTE (else NULL/zero):
*
* joinaliasvars is a list of (usually) Vars corresponding to the columns
* of the join result. An alias Var referencing column K of the join
* result can be replaced by the K'th element of joinaliasvars --- but to
* simplify the task of reverse-listing aliases correctly, we do not do
* that until planning time. In detail: an element of joinaliasvars can
* be a Var of one of the join's input relations, or such a Var with an
* implicit coercion to the join's output column type, or a COALESCE
* expression containing the two input column Vars (possibly coerced).
* Within a Query loaded from a stored rule, it is also possible for
* joinaliasvars items to be null pointers, which are placeholders for
* (necessarily unreferenced) columns dropped since the rule was made.
* Also, once planning begins, joinaliasvars items can be almost anything,
* as a result of subquery-flattening substitutions.
*/
JoinType jointype; /* type of join */
List *joinaliasvars; /* list of alias-var expansions */
/*
* Fields valid for a function RTE (else NIL/zero):
*
* When funcordinality is true, the eref->colnames list includes an alias
* for the ordinality column. The ordinality column is otherwise
* implicit, and must be accounted for "by hand" in places such as
* expandRTE().
*/
List *functions; /* list of RangeTblFunction nodes */
bool funcordinality; /* is this called WITH ORDINALITY? */
/*
* Fields valid for a TableFunc RTE (else NULL):
*/
TableFunc *tablefunc;
/*
* Fields valid for a values RTE (else NIL):
*/
List *values_lists; /* list of expression lists */
/*
* Fields valid for a CTE RTE (else NULL/zero):
*/
char *ctename; /* name of the WITH list item */
Index ctelevelsup; /* number of query levels up */
bool self_reference; /* is this a recursive self-reference? */
/*
* Fields valid for table functions, values, CTE and ENR RTEs (else NIL):
*
* We need these for CTE RTEs so that the types of self-referential
* columns are well-defined. For VALUES RTEs, storing these explicitly
* saves having to re-determine the info by scanning the values_lists. For
* ENRs, we store the types explicitly here (we could get the information
* from the catalogs if 'relid' was supplied, but we'd still need these
* for TupleDesc-based ENRs, so we might as well always store the type
* info here).
*
* For ENRs only, we have to consider the possibility of dropped columns.
* A dropped column is included in these lists, but it will have zeroes in
* all three lists (as well as an empty-string entry in eref). Testing
* for zero coltype is the standard way to detect a dropped column.
*/
List *coltypes; /* OID list of column type OIDs */
List *coltypmods; /* integer list of column typmods */
List *colcollations; /* OID list of column collation OIDs */
/*
* Fields valid for ENR RTEs (else NULL/zero):
*/
char *enrname; /* name of ephemeral named relation */
double enrtuples; /* estimated or actual from caller */
/*
* Fields valid in all RTEs:
*/
Alias *alias; /* user-written alias clause, if any */
Alias *eref; /* expanded reference names */
bool lateral; /* subquery, function, or values is LATERAL? */
bool inh; /* inheritance requested? */
bool inFromCl; /* present in FROM clause? */
AclMode requiredPerms; /* bitmask of required access permissions */
Oid checkAsUser; /* if valid, check access as this role */
Bitmapset *selectedCols; /* columns needing SELECT permission */
Bitmapset *insertedCols; /* columns needing INSERT permission */
Bitmapset *updatedCols; /* columns needing UPDATE permission */
List *securityQuals; /* security barrier quals to apply, if any */
} RangeTblEntry;
FromExpr/JoinExpr
/*
* RangeTblRef - reference to an entry in the query's rangetable
*
* We could use direct pointers to the RT entries and skip having these
* nodes, but multiple pointers to the same node in a querytree cause
* lots of headaches, so it seems better to store an index into the RT.
*/
typedef struct RangeTblRef
{
NodeTag type;
int rtindex;
} RangeTblRef;
/*----------
* JoinExpr - for SQL JOIN expressions
*
* 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.
*
* 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.
*
* 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.
*----------
*/
typedef struct JoinExpr
{
NodeTag type;
JoinType jointype; /* type of join */
bool isNatural; /* Natural join? Will need to shape table */
Node *larg; /* left subtree */
Node *rarg; /* right subtree */
List *usingClause; /* USING clause, if any (list of String) */
Node *quals; /* qualifiers on join, if any */
Alias *alias; /* user-written alias clause, if any */
int rtindex; /* RT index assigned for join, or 0 */
} JoinExpr;
/*----------
* FromExpr - represents a FROM ... WHERE ... construct
*
* 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.
*----------
*/
typedef struct FromExpr
{
NodeTag type;
List *fromlist; /* List of join subtrees */
Node *quals; /* qualifiers on join, if any */
} FromExpr;
TargetEntry
/*--------------------
* TargetEntry -
* a target entry (used in query target lists)
*
* Strictly speaking, a TargetEntry isn't an expression node (since it can't
* be evaluated by ExecEvalExpr). But we treat it as one anyway, since in
* very many places it's convenient to process a whole query targetlist as a
* single expression tree.
*
* In a SELECT's targetlist, resno should always be equal to the item's
* ordinal position (counting from 1). However, in an INSERT or UPDATE
* targetlist, resno represents the attribute number of the destination
* column for the item; so there may be missing or out-of-order resnos.
* It is even legal to have duplicated resnos; consider
* UPDATE table SET arraycol[1] = ..., arraycol[2] = ..., ...
* The two meanings come together in the executor, because the planner
* transforms INSERT/UPDATE tlists into a normalized form with exactly
* one entry for each column of the destination table. Before that's
* happened, however, it is risky to assume that resno == position.
* Generally get_tle_by_resno() should be used rather than list_nth()
* to fetch tlist entries by resno, and only in SELECT should you assume
* that resno is a unique identifier.
*
* resname is required to represent the correct column name in non-resjunk
* entries of top-level SELECT targetlists, since it will be used as the
* column title sent to the frontend. In most other contexts it is only
* a debugging aid, and may be wrong or even NULL. (In particular, it may
* be wrong in a tlist from a stored rule, if the referenced column has been
* renamed by ALTER TABLE since the rule was made. Also, the planner tends
* to store NULL rather than look up a valid name for tlist entries in
* non-toplevel plan nodes.) In resjunk entries, resname should be either
* a specific system-generated name (such as "ctid") or NULL; anything else
* risks confusing ExecGetJunkAttribute!
*
* ressortgroupref is used in the representation of ORDER BY, GROUP BY, and
* DISTINCT items. Targetlist entries with ressortgroupref=0 are not
* sort/group items. If ressortgroupref>0, then this item is an ORDER BY,
* GROUP BY, and/or DISTINCT target value. No two entries in a targetlist
* may have the same nonzero ressortgroupref --- but there is no particular
* meaning to the nonzero values, except as tags. (For example, one must
* not assume that lower ressortgroupref means a more significant sort key.)
* The order of the associated SortGroupClause lists determine the semantics.
*
* resorigtbl/resorigcol identify the source of the column, if it is a
* simple reference to a column of a base table (or view). If it is not
* a simple reference, these fields are zeroes.
*
* If resjunk is true then the column is a working column (such as a sort key)
* that should be removed from the final output of the query. Resjunk columns
* must have resnos that cannot duplicate any regular column's resno. Also
* note that there are places that assume resjunk columns come after non-junk
* columns.
*--------------------
*/
typedef struct TargetEntry
{
Expr xpr;
Expr *expr; /* expression to evaluate */
AttrNumber resno; /* attribute number (see notes above) */
char *resname; /* name of the column (could be NULL) */
Index ressortgroupref; /* nonzero if referenced by a sort/group
* clause */
Oid resorigtbl; /* OID of column's source table */
AttrNumber resorigcol; /* column's number in source table */
bool resjunk; /* set to true to eliminate the attribute from
* final target list */
} TargetEntry;
OpExpr
/*
* OpExpr - expression node for an operator invocation
*
* Semantically, this is essentially the same as a function call.
*
* Note that opfuncid is not necessarily filled in immediately on creation
* of the node. The planner makes sure it is valid before passing the node
* tree to the executor, but during parsing/planning opfuncid can be 0.
*/
typedef struct OpExpr
{
Expr xpr;
Oid opno; /* PG_OPERATOR OID of the operator */
Oid opfuncid; /* PG_PROC OID of underlying function */
Oid opresulttype; /* PG_TYPE OID of result value */
bool opretset; /* true if operator returns set */
Oid opcollid; /* OID of collation of result */
Oid inputcollid; /* OID of collation that operator should use */
List *args; /* arguments to the operator (1 or 2) */
int location; /* token location, or -1 if unknown */
} OpExpr;
三、小結
1、Query樹結構：一棵樹關鍵的資訊包括rtable（相關的資料表或子查詢等）、jointree（連線樹資訊）、targetList（輸出的目標欄位等資訊）等；
2、資料結構：重要的資料結構包括RangeTblEntry、FromExpr、JoinExpr等。
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/6906/viewspace-2374896/，如需轉載，請註明出處，否則將追究法律責任。
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