PostgreSQL聚合函数的实现方法是什么

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一、数据结构

AggState
聚合函数执行时状态结构体,内含AggStatePerAgg等结构体

/* --------------------- *    AggState information * *    ss.ss_ScanTupleSlot refers to output of underlying plan. *  ss.ss_ScanTupleSlot指的是基础计划的输出. *    (ss = ScanState,ps = PlanState) * *    Note: ss.ps.ps_ExprContext contains ecxt_aggvalues and *    ecxt_aggnulls arrays, which hold the computed agg values for the current *    input group during evaluation of an Agg node's output tuple(s).  We *    create a second ExprContext, tmpcontext, in which to evaluate input *    expressions and run the aggregate transition functions. *    注意:ss.ps.ps_ExprContext包含了ecxt_aggvalues和ecxt_aggnulls数组, *      这两个数组保存了在计算agg节点的输出元组时当前输入组已计算的agg值. * --------------------- *//* these structs are private in nodeAgg.c: *///在nodeAgg.c中私有的结构体typedef struct AggStatePerAggData *AggStatePerAgg;typedef struct AggStatePerTransData *AggStatePerTrans;typedef struct AggStatePerGroupData *AggStatePerGroup;typedef struct AggStatePerPhaseData *AggStatePerPhase;typedef struct AggStatePerHashData *AggStatePerHash;typedef struct AggState{    //第一个字段是NodeTag(继承自ScanState)    ScanState    ss;                /* its first field is NodeTag */    //targetlist和quals中所有的Aggref    List       *aggs;            /* all Aggref nodes in targetlist & quals */    //链表的大小(可以为0)    int            numaggs;        /* length of list (could be zero!) */    //pertrans条目大小    int            numtrans;        /* number of pertrans items */    //Agg策略模式    AggStrategy aggstrategy;    /* strategy mode */    //agg-splitting模式,参见nodes.h    AggSplit    aggsplit;        /* agg-splitting mode, see nodes.h */    //指向当前步骤数据的指针    AggStatePerPhase phase;        /* pointer to current phase data */    //步骤数(包括0)    int            numphases;        /* number of phases (including phase 0) */    //当前步骤    int            current_phase;    /* current phase number */    //per-Aggref信息    AggStatePerAgg peragg;        /* per-Aggref information */    //per-Trans状态信息    AggStatePerTrans pertrans;    /* per-Trans state information */    //长生命周期数据的ExprContexts(hashtable)    ExprContext *hashcontext;    /* econtexts for long-lived data (hashtable) */    ////长生命周期数据的ExprContexts(每一个GS使用)    ExprContext **aggcontexts;    /* econtexts for long-lived data (per GS) */    //输入表达式的ExprContext    ExprContext *tmpcontext;    /* econtext for input expressions */#define FIELDNO_AGGSTATE_CURAGGCONTEXT 14    //当前活跃的aggcontext    ExprContext *curaggcontext; /* currently active aggcontext */    //当前活跃的aggregate(如存在)    AggStatePerAgg curperagg;    /* currently active aggregate, if any */#define FIELDNO_AGGSTATE_CURPERTRANS 16    //当前活跃的trans state    AggStatePerTrans curpertrans;    /* currently active trans state, if any */    //输入结束?    bool        input_done;        /* indicates end of input */    //Agg扫描结束?    bool        agg_done;        /* indicates completion of Agg scan */    //最后一个grouping set    int            projected_set;    /* The last projected grouping set */#define FIELDNO_AGGSTATE_CURRENT_SET 20    //将要解析的当前grouping set    int            current_set;    /* The current grouping set being evaluated */    //当前投影操作的分组列    Bitmapset  *grouped_cols;    /* grouped cols in current projection */    //倒序的分组列链表    List       *all_grouped_cols;    /* list of all grouped cols in DESC order */    /* These fields are for grouping set phase data */    //-------- 下面的列用于grouping set步骤数据    //所有步骤中最大的sets大小    int            maxsets;        /* The max number of sets in any phase */    //所有步骤的数组    AggStatePerPhase phases;    /* array of all phases */    //对于phases > 1,已排序的输入信息    Tuplesortstate *sort_in;    /* sorted input to phases > 1 */    //对于下一个步骤,输入已拷贝    Tuplesortstate *sort_out;    /* input is copied here for next phase */    //排序结果的slot    TupleTableSlot *sort_slot;    /* slot for sort results */    /* these fields are used in AGG_PLAIN and AGG_SORTED modes: */    //------- 下面的列用于AGG_PLAIN和AGG_SORTED模式:    //per-group指针的grouping set编号数组    AggStatePerGroup *pergroups;    /* grouping set indexed array of per-group                                     * pointers */    //当前组的第一个元组拷贝    HeapTuple    grp_firstTuple; /* copy of first tuple of current group */    /* these fields are used in AGG_HASHED and AGG_MIXED modes: */    //--------- 下面的列用于AGG_HASHED和AGG_MIXED模式:    //是否已填充hash表?    bool        table_filled;    /* hash table filled yet? */    //hash桶数?    int            num_hashes;    //相应的哈希表数据数组    AggStatePerHash perhash;    /* array of per-hashtable data */    //per-group指针的grouping set编号数组    AggStatePerGroup *hash_pergroup;    /* grouping set indexed array of                                         * per-group pointers */    /* support for evaluation of agg input expressions: */    //---------- agg输入表达式解析支持#define FIELDNO_AGGSTATE_ALL_PERGROUPS 34    //首先是->pergroups,然后是hash_pergroup    AggStatePerGroup *all_pergroups;    /* array of first ->pergroups, than                                         * ->hash_pergroup */    //投影实现机制    ProjectionInfo *combinedproj;    /* projection machinery */} AggState;/* Primitive options supported by nodeAgg.c: *///nodeag .c支持的基本选项#define AGGSPLITOP_COMBINE        0x01    /* substitute combinefn for transfn */#define AGGSPLITOP_SKIPFINAL    0x02    /* skip finalfn, return state as-is */#define AGGSPLITOP_SERIALIZE    0x04    /* apply serializefn to output */#define AGGSPLITOP_DESERIALIZE    0x08    /* apply deserializefn to input *//* Supported operating modes (i.e., useful combinations of these options): *///支持的操作模式typedef enum AggSplit{    /* Basic, non-split aggregation: */    //基本 : 非split聚合    AGGSPLIT_SIMPLE = 0,    /* Initial phase of partial aggregation, with serialization: */    //部分聚合的初始步骤,序列化    AGGSPLIT_INITIAL_SERIAL = AGGSPLITOP_SKIPFINAL | AGGSPLITOP_SERIALIZE,    /* Final phase of partial aggregation, with deserialization: */    //部分聚合的最终步骤,反序列化    AGGSPLIT_FINAL_DESERIAL = AGGSPLITOP_COMBINE | AGGSPLITOP_DESERIALIZE} AggSplit;/* Test whether an AggSplit value selects each primitive option: *///测试AggSplit选择了哪些基本选项#define DO_AGGSPLIT_COMBINE(as)        (((as) & AGGSPLITOP_COMBINE) != 0)#define DO_AGGSPLIT_SKIPFINAL(as)    (((as) & AGGSPLITOP_SKIPFINAL) != 0)#define DO_AGGSPLIT_SERIALIZE(as)    (((as) & AGGSPLITOP_SERIALIZE) != 0)#define DO_AGGSPLIT_DESERIALIZE(as) (((as) & AGGSPLITOP_DESERIALIZE) != 0)

二、源码解读

N/A

三、跟踪分析

跟踪分析数据结构中的相关信息.
测试数据:

-- 禁用并行set max_parallel_workers_per_gather=0;select bh,avg(c1),min(c1),max(c2) from t_agg_simple group by bh;

aggstate是聚合运算的运行状态.

1536        AggState   *node = castNode(AggState, pstate);(gdb) n1537        TupleTableSlot *result = NULL;(gdb) p *node$1 = {ss = {ps = {type = T_AggState, plan = 0x120ba30, state = 0x12eb428, ExecProcNode = 0x6ee438 ,       ExecProcNodeReal = 0x6ee438 , instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0,       qual = 0x0, lefttree = 0x12ebbb0, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0,       ps_ResultTupleSlot = 0x12ec7b0, ps_ExprContext = 0x12ebaf0, ps_ProjInfo = 0x12ec8f0, scandesc = 0x12ebf00},     ss_currentRelation = 0x0, ss_currentScanDesc = 0x0, ss_ScanTupleSlot = 0x12ec458}, aggs = 0x12ece00, numaggs = 3,   numtrans = 3, aggstrategy = AGG_HASHED, aggsplit = AGGSPLIT_SIMPLE, phase = 0x12ecef8, numphases = 1, current_phase = 0,   peragg = 0x13083e0, pertrans = 0x130a3f0, hashcontext = 0x12eba30, aggcontexts = 0x12eb858, tmpcontext = 0x12eb878,   curaggcontext = 0x12eba30, curperagg = 0x0, curpertrans = 0x0, input_done = false, agg_done = false, projected_set = -1,   current_set = 0, grouped_cols = 0x0, all_grouped_cols = 0x12ed090, maxsets = 1, phases = 0x12ecef8, sort_in = 0x0,   sort_out = 0x0, sort_slot = 0x0, pergroups = 0x0, grp_firstTuple = 0x0, table_filled = false, num_hashes = 1,   perhash = 0x12ecf50, hash_pergroup = 0x13085f8, all_pergroups = 0x13085f8, combinedproj = 0x0}

aggstate->phase/phases是当前阶段/所有阶段的信息.
在本例中,由于只有一个阶段:AGG_HASHED,因此两者是一样的.

(gdb) p *node->phase$2 = {aggstrategy = AGG_HASHED, numsets = 1, gset_lengths = 0x12ecfe8, grouped_cols = 0x12ed008, eqfunctions = 0x0,   aggnode = 0x120ba30, sortnode = 0x0, evaltrans = 0x1315800}(gdb) p node->phases[0]$27 = {aggstrategy = AGG_HASHED, numsets = 1, gset_lengths = 0x12ecfe8, grouped_cols = 0x12ed008, eqfunctions = 0x0,   aggnode = 0x120ba30, sortnode = 0x0, evaltrans = 0x1315800}

aggstate->phase->evaltrans是该阶段的表达式解析转换函数.
在本例中,该函数是ExecInterpExpr(通过执行一系列的步骤得到值)

(gdb) p *node->phase->evaltrans$3 = {tag = {type = T_ExprState}, flags = 6 '\006', resnull = false, resvalue = 0, resultslot = 0x0, steps = 0x1315ac0,   evalfunc = 0x6cd882 , expr = 0x12eb640, evalfunc_private = 0x6cb43e ,   steps_len = 16, steps_alloc = 16, parent = 0x12eb640, ext_params = 0x0, innermost_caseval = 0x0,   innermost_casenull = 0x0, innermost_domainval = 0x0, innermost_domainnull = 0x0}

aggstate->phase->evaltrans是该阶段的聚合节点,即T_AGG.

(gdb) p *node->phase->aggnode$9 = {plan = {type = T_Agg, startup_cost = 24.800000000000001, total_cost = 27.300000000000001, plan_rows = 200,     plan_width = 98, parallel_aware = false, parallel_safe = false, plan_node_id = 0, targetlist = 0x12fbf10, qual = 0x0,     lefttree = 0x12fb9d0, righttree = 0x0, initPlan = 0x0, extParam = 0x0, allParam = 0x0}, aggstrategy = AGG_HASHED,   aggsplit = AGGSPLIT_SIMPLE, numCols = 1, grpColIdx = 0x12fbcc0, grpOperators = 0x12fbca0, numGroups = 200,   aggParams = 0x0, groupingSets = 0x0, chain = 0x0}

aggstate->peragg存储的是per-Aggref信息,亦即每一个聚合对应一个,每一个peragg->aggref对应一个聚合信息.
第1个是max:

(gdb) p *node->peragg$10 = {aggref = 0x12fc458, transno = 0, finalfn_oid = 0, finalfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0,     fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0},   numFinalArgs = 1, aggdirectargs = 0x0, resulttypeLen = 4, resulttypeByVal = true, shareable = true}(gdb) p *node->peragg->aggref$11 = {xpr = {type = T_Aggref}, aggfnoid = 2116, aggtype = 23, aggcollid = 0, inputcollid = 0, aggtranstype = 23,   aggargtypes = 0x12fc518, aggdirectargs = 0x0, args = 0x12fc628, aggorder = 0x0, aggdistinct = 0x0, aggfilter = 0x0,   aggstar = false, aggvariadic = false, aggkind = 110 'n', agglevelsup = 0, aggsplit = AGGSPLIT_SIMPLE, location = 26}########  testdb=# select oid,proname from pg_proc where oid in (2116,768); oid  |  proname   ------+------------  768 | int4larger 2116 | max(2 rows)########

第2个是min:

(gdb) p node->peragg[1]$38 = {aggref = 0x12fc1d0, transno = 1, finalfn_oid = 0, finalfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0,     fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0},   numFinalArgs = 1, aggdirectargs = 0x0, resulttypeLen = 4, resulttypeByVal = true, shareable = true}(gdb) p *node->peragg[1]->aggref$39 = {xpr = {type = T_Aggref}, aggfnoid = 2132, aggtype = 23, aggcollid = 0, inputcollid = 0, aggtranstype = 23,   aggargtypes = 0x12fc290, aggdirectargs = 0x0, args = 0x12fc3a0, aggorder = 0x0, aggdistinct = 0x0, aggfilter = 0x0,   aggstar = false, aggvariadic = false, aggkind = 110 'n', agglevelsup = 0, aggsplit = AGGSPLIT_SIMPLE, location = 18}############testdb=# select oid,proname from pg_proc where oid in (2132,769); oid  |   proname   ------+-------------  769 | int4smaller 2132 | min(2 rows)###########

第3个是avg:

(gdb) p node->peragg[2]$40 = {aggref = 0x12fbf48, transno = 2, finalfn_oid = 1964, finalfn = {fn_addr = 0x978251 , fn_oid = 1964,     fn_nargs = 1, fn_strict = true, fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x12eb310,     fn_expr = 0x1315698}, numFinalArgs = 1, aggdirectargs = 0x0, resulttypeLen = -1, resulttypeByVal = false,   shareable = true}(gdb) p *node->peragg[2]->aggref$41 = {xpr = {type = T_Aggref}, aggfnoid = 2101, aggtype = 1700, aggcollid = 0, inputcollid = 0, aggtranstype = 1016,   aggargtypes = 0x12fc008, aggdirectargs = 0x0, args = 0x12fc118, aggorder = 0x0, aggdistinct = 0x0, aggfilter = 0x0,   aggstar = false, aggvariadic = false, aggkind = 110 'n', agglevelsup = 0, aggsplit = AGGSPLIT_SIMPLE, location = 10}#####testdb=# select oid,proname from pg_proc where oid in (2101,1963); oid  |    proname     ------+---------------- 1963 | int4_avg_accum 2101 | avg(2 rows)#####

aggstate->pertrans保存的是转换函数.
第1/2/3个分别是int4larger/int4smaller/int4_avg_accum

(gdb) p node->pertrans[0]$19 = {aggref = 0x12fc458, aggshared = false, numInputs = 1, numTransInputs = 1, transfn_oid = 768, serialfn_oid = 0,   deserialfn_oid = 0, aggtranstype = 23, transfn = {fn_addr = 0x93e877 , fn_oid = 768, fn_nargs = 2,     fn_strict = true, fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x12eb310, fn_expr = 0x1315458},   serialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000',     fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, deserialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0,     fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0},   aggCollation = 0, numSortCols = 0, numDistinctCols = 0, sortColIdx = 0x0, sortOperators = 0x0, sortCollations = 0x0,   sortNullsFirst = 0x0, equalfnOne = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false,     fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, equalfnMulti = 0x0, initValue = 0,   initValueIsNull = true, inputtypeLen = 0, transtypeLen = 4, inputtypeByVal = false, transtypeByVal = true,   sortslot = 0x0, uniqslot = 0x0, sortdesc = 0x0, sortstates = 0x1308620, transfn_fcinfo = {flinfo = 0x130a418,     context = 0x12eb640, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 2, arg = {0 },     argnull = {false }}, serialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0,     fncollation = 0, isnull = false, nargs = 0, arg = {0 }, argnull = {false }},   deserialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 0, arg = {      0 }, argnull = {false }}}(gdb) p node->pertrans[1]$20 = {aggref = 0x12fc1d0, aggshared = false, numInputs = 1, numTransInputs = 1, transfn_oid = 769, serialfn_oid = 0,   deserialfn_oid = 0, aggtranstype = 23, transfn = {fn_addr = 0x93e8a3 , fn_oid = 769, fn_nargs = 2,     fn_strict = true, fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x12eb310, fn_expr = 0x13155a8},   serialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000',     fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, deserialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0,     fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0},   aggCollation = 0, numSortCols = 0, numDistinctCols = 0, sortColIdx = 0x0, sortOperators = 0x0, sortCollations = 0x0,   sortNullsFirst = 0x0, equalfnOne = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false,     fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, equalfnMulti = 0x0, initValue = 0,   initValueIsNull = true, inputtypeLen = 0, transtypeLen = 4, inputtypeByVal = false, transtypeByVal = true,   sortslot = 0x0, uniqslot = 0x0, sortdesc = 0x0, sortstates = 0x1308640, transfn_fcinfo = {flinfo = 0x130b060,     context = 0x12eb640, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 2, arg = {0 },     argnull = {false }}, serialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0,     fncollation = 0, isnull = false, nargs = 0, arg = {0 }, argnull = {false }},   deserialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 0, arg = {      0 }, argnull = {false }}}(gdb) p node->pertrans[2]$21 = {aggref = 0x12fbf48, aggshared = false, numInputs = 1, numTransInputs = 1, transfn_oid = 1963, serialfn_oid = 0,   deserialfn_oid = 0, aggtranstype = 1016, transfn = {fn_addr = 0x977d8f , fn_oid = 1963, fn_nargs = 2,     fn_strict = true, fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x12eb310, fn_expr = 0x1315a68},   serialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000',     fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, deserialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0,     fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0},   aggCollation = 0, numSortCols = 0, numDistinctCols = 0, sortColIdx = 0x0, sortOperators = 0x0, sortCollations = 0x0,   sortNullsFirst = 0x0, equalfnOne = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false,     fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, equalfnMulti = 0x0, initValue = 20010920,   initValueIsNull = false, inputtypeLen = 0, transtypeLen = -1, inputtypeByVal = false, transtypeByVal = false,   sortslot = 0x0, uniqslot = 0x0, sortdesc = 0x0, sortstates = 0x13156f0, transfn_fcinfo = {flinfo = 0x130bca8,     context = 0x12eb640, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 2, arg = {0 },     argnull = {false }}, serialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0,     fncollation = 0, isnull = false, nargs = 0, arg = {0 }, argnull = {false }},   deserialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 0, arg = {      0 }, argnull = {false }}}

aggstate->perhash存储的是per-hashtable数据.perhash->hashslot存储的是最小化Tuple.
本例只有一个group set,因此对应的hash表只有一个.

(gdb) p node->perhash[0]$30 = {hashtable = 0x1308890, hashiter = {cur = 0, end = 0, done = false}, hashslot = 0x12ed238, hashfunctions = 0x12ed2d0,   eqfuncoids = 0x1308700, numCols = 1, numhashGrpCols = 1, largestGrpColIdx = 1, hashGrpColIdxInput = 0x1308660,   hashGrpColIdxHash = 0x1308680, aggnode = 0x120ba30}(gdb) p node->perhash[0]->hashslot[0]$32 = {type = T_TupleTableSlot, tts_isempty = true, tts_shouldFree = false, tts_shouldFreeMin = false, tts_slow = false,   tts_tuple = 0x0, tts_tupleDescriptor = 0x12ed120, tts_mcxt = 0x12eb310, tts_buffer = 0, tts_nvalid = 0,   tts_values = 0x12ed298, tts_isnull = 0x12ed2a0, tts_mintuple = 0x0, tts_minhdr = {t_len = 0, t_self = {ip_blkid = {        bi_hi = 0, bi_lo = 0}, ip_posid = 0}, t_tableOid = 0, t_data = 0x0}, tts_off = 0, tts_fixedTupleDescriptor = true}

其他的数据结构.
aggstate->hash_pergroup/all_pergroups/combinedproj

(gdb) p node->hash_pergroup$35 = (AggStatePerGroup *) 0x13085f8(gdb) p *node->hash_pergroup$36 = (AggStatePerGroup) 0x0(gdb) p *node->all_pergroups$37 = (AggStatePerGroup) 0x0(gdb) p *node->combinedprojCannot access memory at address 0x0

简单来说,整个过程大体如下:
每个Group的列信息会存储在aggstate->perhash中,按阶段(aggstate->phases)逐个执行.
扫描数据表,在遍历tuple的时候,通过hash函数比对(Key为最小化tuple)找到/创建相应的Group组aggstate->perhash(hash table),提取tuple中相应的列值作为参数输入到aggstate->pertrans中定义的转换函数中,解析执行结果并存储,最后执行投影操作,把最终结果返回给客户端

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