PostgreSQL 原始碼解讀（19）- 查詢語句#4（ParseTree詳解）

本文簡單介紹了PG解析查詢語句後生成的解析樹Parsetree的詳細結構。詞法和語法解析是執行SQL的第一步，解析樹Parsetree是後續查詢重寫優化、生成計劃等步驟的輸入資訊。

一、解析樹結構

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.

Breakpoint 1, exec_simple_query (
    query_string=0x1641ef0 "select * from (\nselect t_dwxx.dwmc,t_grxx.grbh,t_grxx.xm,t_jfxx.ny,t_jfxx.je\nfrom t_dwxx inner join t_grxx on t_dwxx.dwbh = t_grxx.dwbh\ninner join t_jfxx on t_grxx.grbh = t_jfxx.grbh\nwhere t_dwxx.dwbh"...) at postgres.c:893
944     parsetree_list = pg_parse_query(query_string);
(gdb) 
947     if (check_log_statement(parsetree_list))
#解析樹中只有一個元素
(gdb) p *parsetree_list
$2 = {type = T_List, length = 1, head = 0x1667180, tail = 0x1667180}
(gdb) p *(Node *)(parsetree_list->head.data->ptr_value) #獲得List中的節點型別
$3 = {type = T_RawStmt}
(gdb) p *(RawStmt *)(parsetree_list->head.data->ptr_value)
$4 = {type = T_RawStmt, stmt = 0x1666df0, stmt_location = 0, stmt_len = 455}
(gdb) p *(((RawStmt *)(parsetree_list->head.data->ptr_value))->stmt) #獲得實際的stmt型別
$5 = {type = T_SelectStmt}
(gdb) set $stmt=(SelectStmt *)(((RawStmt *)(parsetree_list->head.data->ptr_value))->stmt) #設定臨時變數
(gdb) p *$stmt
$6 = {type = T_SelectStmt, distinctClause = 0x0, intoClause = 0x0, targetList = 0x1642ba0, 
  fromClause = 0x1666dc0, whereClause = 0x0, groupClause = 0x0, havingClause = 0x0, windowClause = 0x0, 
  valuesLists = 0x0, sortClause = 0x1667080, limitOffset = 0x0, limitCount = 0x16670b0, lockingClause = 0x0, 
  withClause = 0x0, op = SETOP_NONE, all = false, larg = 0x0, rarg = 0x0}
#op = SETOP_NONE,集合操作為NONE,只有一個SelectStmt,因此larg&rarg(型別為SelectStmt)為NULL
#------------------->targetList 
(gdb) p *($stmt->targetList)
$7 = {type = T_List, length = 1, head = 0x1642b80, tail = 0x1642b80}
(gdb) p *(Node *)($stmt->targetList->head.data->ptr_value)
$8 = {type = T_ResTarget}
(gdb) set $restarget=(ResTarget *)($stmt->targetList->head.data->ptr_value)
(gdb) p *$restarget->val
$9 = {type = T_ColumnRef}
(gdb) p *(ColumnRef *)$restarget->val
$10 = {type = T_ColumnRef, fields = 0x1642b00, location = 7}
(gdb) p *((ColumnRef *)$restarget->val)->fields
$11 = {type = T_List, length = 1, head = 0x1642ae0, tail = 0x1642ae0}
(gdb) p *(Node *)(((ColumnRef *)$restarget->val)->fields)->head.data->ptr_value
$12 = {type = T_A_Star}
#實際型別是A_Star,即"*"
(gdb) p *(A_Star *)(((ColumnRef *)$restarget->val)->fields)->head.data->ptr_value
$14 = {type = T_A_Star}

#------------------->fromClause 
(gdb) p *$stmt->fromClause
{type = T_List, length = 1, head = 0x1666da0, tail = 0x1666da0}
(gdb) p *(Node *)($stmt->fromClause->head.data->ptr_value)
$15 = {type = T_RangeSubselect} #實際型別是範圍子查詢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,子查詢是SelectStmt型別的節點
$17 = {type = T_SelectStmt}
(gdb) p *($fromclause->alias) #alias,別名,實際值是字串ret
$18 = {type = T_Alias, aliasname = 0x1666d28 "ret", colnames = 0x0}
#檢視子查詢結構體資訊
#集合操作是SETOP_UNION,並∪操作,並操作的子查詢在larg和rarg中
(gdb) p *(SelectStmt *)($fromclause->subquery)
$20 = {type = T_SelectStmt, distinctClause = 0x0, intoClause = 0x0, targetList = 0x0, fromClause = 0x0, 
  whereClause = 0x0, groupClause = 0x0, havingClause = 0x0, windowClause = 0x0, valuesLists = 0x0, 
  sortClause = 0x0, limitOffset = 0x0, limitCount = 0x0, lockingClause = 0x0, withClause = 0x0, 
  op = SETOP_UNION, all = true, larg = 0x1665818, rarg = 0x1666b08}
#--->larg,左樹節點
(gdb)  p *((SelectStmt *)($fromclause->subquery))->larg
$21 = {type = T_SelectStmt, distinctClause = 0x0, intoClause = 0x0, targetList = 0x1642d50, 
  fromClause = 0x1643b38, whereClause = 0x1643d10, groupClause = 0x0, havingClause = 0x0, windowClause = 0x0, 
  valuesLists = 0x0, sortClause = 0x0, limitOffset = 0x0, limitCount = 0x0, lockingClause = 0x0, 
  withClause = 0x0, op = SETOP_NONE, all = false, larg = 0x0, rarg = 0x0}
(gdb) set $subquerylarg=((SelectStmt *)($fromclause->subquery))->larg
#->targetList
(gdb) p *$subquerylarg->targetList
$25 = {type = T_List, length = 5, head = 0x1642d30, tail = 0x1643360}
(gdb) p *(Node *)($subquerylarg->targetList->head.data->ptr_value)
$26 = {type = T_ResTarget}
(gdb) set $subvar=(ResTarget *)($subquerylarg->targetList->head.data->ptr_value)
(gdb) p *$subvar 
{type = T_ResTarget, name = 0x0, indirection = 0x0, val = 0x1642c70, location = 23}
(gdb) p *($subvar->val)
$29 = {type = T_ColumnRef}
(gdb) p *(ColumnRef *)($subvar->val)
$30 = {type = T_ColumnRef, fields = 0x1642c40, location = 23}
(gdb) p *(Node *)(((ColumnRef *)($subvar->val))->fields)->head.data->ptr_value
$33 = {type = T_String}
(gdb) p *(Value *)(((ColumnRef *)($subvar->val))->fields)->head.data->ptr_value
$34 = {type = T_String, val = {ival = 23342032, str = 0x1642bd0 "t_dwxx"}}
(gdb) p *(Value *)(((ColumnRef *)($subvar->val))->fields)->tail.data->ptr_value
$36 = {type = T_String, val = {ival = 23342056, str = 0x1642be8 "dwmc"}}
#->fromClause
(gdb) p *($subquerylarg->fromClause)
$37 = {type = T_List, length = 1, head = 0x1643b18, tail = 0x1643b18}
(gdb) p *(Node *)(($subquerylarg->fromClause)->head.data->ptr_value)
$38 = {type = T_JoinExpr}
(gdb) p *(JoinExpr *)(($subquerylarg->fromClause)->head.data->ptr_value)
$39 = {type = T_JoinExpr, jointype = JOIN_INNER, isNatural = false, larg = 0x1643730, rarg = 0x1643798, 
  usingClause = 0x0, quals = 0x1643a08, alias = 0x0, rtindex = 0}
(gdb) set $joinexpr=(JoinExpr *)(($subquerylarg->fromClause)->head.data->ptr_value)
(gdb) p *($joinexpr->larg)
$41 = {type = T_JoinExpr}
(gdb) p *(JoinExpr *)($joinexpr->larg)
$42 = {type = T_JoinExpr, jointype = JOIN_INNER, isNatural = false, larg = 0x1643398, rarg = 0x1643400, 
  usingClause = 0x0, quals = 0x1643670, alias = 0x0, rtindex = 0}
(gdb) p *((JoinExpr *)($joinexpr->larg))->larg
$43 = {type = T_RangeVar}
(gdb) p *(RangeVar *)((JoinExpr *)($joinexpr->larg))->larg
$44 = {type = T_RangeVar, catalogname = 0x0, schemaname = 0x0, relname = 0x1643380 "t_dwxx", inh = true, 
  relpersistence = 112 'p', alias = 0x0, location = 82}
(gdb) p *((JoinExpr *)($joinexpr->larg))->rarg
$45 = {type = T_RangeVar}
(gdb) p *(RangeVar *)((JoinExpr *)($joinexpr->larg))->rarg
$46 = {type = T_RangeVar, catalogname = 0x0, schemaname = 0x0, relname = 0x16433e8 "t_grxx", inh = true, 
  relpersistence = 112 'p', alias = 0x0, location = 100}
(gdb) set $expr=(A_Expr *)((JoinExpr *)($joinexpr->larg))->quals
(gdb) p *(Value *) $expr->name->head->data.ptr_value
{type = T_String, val = {ival = 11157870, str = 0xaa416e "="}}
(gdb) p *(Value *)(((ColumnRef *)$expr->lexpr)->fields->head->data.ptr_value)
{type = T_String, val = {ival = 23344208, str = 0x1643450 "t_dwxx"}}
(gdb) p *(Value *)(((ColumnRef *)$expr->lexpr)->fields->tail->data.ptr_value)
{type = T_String, val = {ival = 23344232, str = 0x1643468 "dwbh"}}
(gdb) p *(Value *)(((ColumnRef *)$expr->rexpr)->fields->head->data.ptr_value)
 {type = T_String, val = {ival = 23344480, str = 0x1643560 "t_grxx"}}
(gdb) p *(Value *)(((ColumnRef *)$expr->rexpr)->fields->tail->data.ptr_value)
{type = T_String, val = {ival = 23344504, str = 0x1643578 "dwbh"}}

(gdb) p *($joinexpr->rarg)
$47 = {type = T_RangeVar}
(gdb) p *(RangeVar *)($joinexpr->rarg)
$48 = {type = T_RangeVar, catalogname = 0x0, schemaname = 0x0, relname = 0x1643780 "t_jfxx", inh = true, 
  relpersistence = 112 'p', alias = 0x0, location = 147}
(gdb) p *($joinexpr->quals)
$49 = {type = T_A_Expr}
(gdb) p *(A_Expr *)($joinexpr->quals)
$51 = {type = T_A_Expr, kind = AEXPR_OP, name = 0x1643a98, lexpr = 0x1643888, rexpr = 0x1643998, 
  location = 169}(gdb) 
(gdb) p *((A_Expr *)($joinexpr->quals))->name
$52 = {type = T_List, length = 1, head = 0x1643a78, tail = 0x1643a78}
(gdb) set $expr=(A_Expr *)($joinexpr->quals)
(gdb) p *(Node *)($expr->name->head.data->ptr_value)
$53 = {type = T_String}
(gdb) p *(Value *)($expr->name->head.data->ptr_value)
$54 = {type = T_String, val = {ival = 11157870, str = 0xaa416e "="}}
(gdb) p *($expr->lexpr)
$55 = {type = T_ColumnRef}
(gdb) p *(Value *)(((ColumnRef *)$expr->lexpr)->fields->head->data.ptr_value)
$56 = {type = T_String, val = {ival = 23345128, str = 0x16437e8 "t_grxx"}}
(gdb) p *(Value *)(((ColumnRef *)$expr->lexpr)->fields->tail->data.ptr_value)
$57 = {type = T_String, val = {ival = 23345152, str = 0x1643800 "grbh"}}
(gdb) p *($expr->rexpr)
$58 = {type = T_ColumnRef}
(gdb) p *(Value *)(((ColumnRef *)$expr->rexpr)->fields->head->data.ptr_value)
$59 = {type = T_String, val = {ival = 23345400, str = 0x16438f8 "t_jfxx"}}
(gdb) p *(Value *)(((ColumnRef *)$expr->rexpr)->fields->tail->data.ptr_value)
$60 = {type = T_String, val = {ival = 23345424, str = 0x1643910 "grbh"}}

#--->rarg,右樹節點
#參見larg

#------------------->sortClause 
(gdb) p *$stmt->sortClause
$67 = {type = T_List, length = 1, head = 0x1667060, tail = 0x1667060}
(gdb) p *(Node *)$stmt->sortClause->head.data->ptr_value
$69 = {type = T_SortBy}
(gdb) p *(SortBy *)$stmt->sortClause->head.data->ptr_value
$70 = {type = T_SortBy, node = 0x1666fa0, sortby_dir = SORTBY_DEFAULT, sortby_nulls = SORTBY_NULLS_DEFAULT, 
  useOp = 0x0, location = -1}
(gdb) p *(SortBy *)$stmt->sortClause->head.data->ptr_value
$71 = {type = T_SortBy, node = 0x1666fa0, sortby_dir = SORTBY_DEFAULT, sortby_nulls = SORTBY_NULLS_DEFAULT, 
  useOp = 0x0, location = -1}
(gdb) set $sortby=(SortBy *)$stmt->sortClause->head.data->ptr_value
(gdb) p *$sortby->node
$72 = {type = T_ColumnRef}
(gdb) p *(Value *)(((ColumnRef *)$sortby->node)->fields->head->data.ptr_value)
$74 = {type = T_String, val = {ival = 23490304, str = 0x1666f00 "ret"}}
(gdb) p *(Value *)(((ColumnRef *)$sortby->node)->fields->head->next.data.ptr_value)
$75 = {type = T_String, val = {ival = 23490328, str = 0x1666f18 "grbh"}}

#------------------->limitCount 
(gdb)  p *$stmt->limitCount
$78 = {type = T_A_Const}
(gdb)  p *(A_Const *)$stmt->limitCount
$79 = {type = T_A_Const, val = {type = T_Integer, val = {ival = 4, str = 0x4 <Address 0x4 out of bounds>}}, 
  location = 454}

最終的解析樹如下圖所示:

解析樹

二、資料結構

1、SelectStmt

/* ----------------------
  *      Select Statement
  *
  * A "simple" SELECT is represented in the output of gram.y by a single
  * SelectStmt node; so is a VALUES construct.  A query containing set
  * operators (UNION, INTERSECT, EXCEPT) is represented by a tree of SelectStmt
  * nodes, in which the leaf nodes are component SELECTs and the internal nodes
  * represent UNION, INTERSECT, or EXCEPT operators.  Using the same node
  * type for both leaf and internal nodes allows gram.y to stick ORDER BY,
  * LIMIT, etc, clause values into a SELECT statement without worrying
  * whether it is a simple or compound SELECT.
  * ----------------------
  */
 typedef enum SetOperation
 {
     SETOP_NONE = 0,
     SETOP_UNION,
     SETOP_INTERSECT,
     SETOP_EXCEPT
 } SetOperation;
 
 typedef struct SelectStmt
 {
     NodeTag     type;
 
     /*
      * These fields are used only in "leaf" SelectStmts.
      */
     List       *distinctClause; /* NULL, list of DISTINCT ON exprs, or
                                  * lcons(NIL,NIL) for all (SELECT DISTINCT) */
     IntoClause *intoClause;     /* target for SELECT INTO */
     List       *targetList;     /* the target list (of ResTarget) */
     List       *fromClause;     /* the FROM clause */
     Node       *whereClause;    /* WHERE qualification */
     List       *groupClause;    /* GROUP BY clauses */
     Node       *havingClause;   /* HAVING conditional-expression */
     List       *windowClause;   /* WINDOW window_name AS (...), ... */
 
     /*
      * In a "leaf" node representing a VALUES list, the above fields are all
      * null, and instead this field is set.  Note that the elements of the
      * sublists are just expressions, without ResTarget decoration. Also note
      * that a list element can be DEFAULT (represented as a SetToDefault
      * node), regardless of the context of the VALUES list. It's up to parse
      * analysis to reject that where not valid.
      */
     List       *valuesLists;    /* untransformed list of expression lists */
 
     /*
      * These fields are used in both "leaf" SelectStmts and upper-level
      * SelectStmts.
      */
     List       *sortClause;     /* sort clause (a list of SortBy's) */
     Node       *limitOffset;    /* # of result tuples to skip */
     Node       *limitCount;     /* # of result tuples to return */
     List       *lockingClause;  /* FOR UPDATE (list of LockingClause's) */
     WithClause *withClause;     /* WITH clause */
 
     /*
      * These fields are used only in upper-level SelectStmts.
      */
     SetOperation op;            /* type of set op */
     bool        all;            /* ALL specified? */
     struct SelectStmt *larg;    /* left child */
     struct SelectStmt *rarg;    /* right child */
     /* Eventually add fields for CORRESPONDING spec here */
 } SelectStmt;

2、RangeSubselect

 /*
  * RangeSubselect - subquery appearing in a FROM clause
  */
 typedef struct RangeSubselect
 {
     NodeTag     type;
     bool        lateral;        /* does it have LATERAL prefix? */
     Node       *subquery;       /* the untransformed sub-select clause */
     Alias      *alias;          /* table alias & optional column aliases */
 } RangeSubselect;

3、Alias

/*
  * Alias -
  *    specifies an alias for a range variable; the alias might also
  *    specify renaming of columns within the table.
  *
  * 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.
  */
 typedef struct Alias
 {
     NodeTag     type;
     char       *aliasname;      /* aliased rel name (never qualified) */
     List       *colnames;       /* optional list of column aliases */
 } Alias;

4、ResTarget

 /*
  * ResTarget -
  *    result target (used in target list of pre-transformed parse trees)
  *
  * 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.
  *
  * 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.
  *
  * 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.
  *
  * See A_Indirection for more info about what can appear in 'indirection'.
  */
 typedef struct ResTarget
 {
     NodeTag     type;
     char       *name;           /* column name or NULL */
     List       *indirection;    /* subscripts, field names, and '*', or NIL */
     Node       *val;            /* the value expression to compute or assign */
     int         location;       /* token location, or -1 if unknown */
 } ResTarget;

5、FromExpr

 /*----------
  * 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;

6、JoinExpr

 /*----------
  * 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;
 

7、RangeVar

 /*
  * RangeVar - range variable, used in FROM clauses
  *
  * 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.
  */
 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;

8、ColumnRef

 /*
  * ColumnRef - specifies a reference to a column, or possibly a whole tuple
  *
  * 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!
  *
  * Note: any array 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;
     List       *fields;         /* field names (Value strings) or A_Star */
     int         location;       /* token location, or -1 if unknown */
 } ColumnRef;

三、小結

1、解析樹：通過跟蹤分析原始碼，分析解析樹Parsetree的結構；
2、其他資料結構：SelectSmt、RangeSubselect、JoinExpr等資料結構。