Parser

1. 相关函数: pg_parse_query

2. 核心结构

RawStmt: container for any one statement's raw parse tree

stmtmulti /* list */
    toplevel_stmt /* aka: RawStmt */
        Stmt /* regular SQL statement: START TRANSACTION; */
            SelectStmt
            InsertStmt
            DeleteStmt
            UpdateStmt
            MergeStmt
            /*...*/
        TransactionStmtLegacy /* Legacy transaction statement (BEGIN) for PG compatibility */

typedef struct RawStmt
{
    pg_node_attr(no_query_jumble)

    NodeTag     type;
    Node       *stmt;           /* raw parse tree */
    int         stmt_location;  /* start location, or -1 if unknown */
    int         stmt_len;       /* length in bytes; 0 means "rest of string" */
} RawStmt;

SelectStmt

SelectStmt
    select_no_parens
        simple_select
            SELECT opt_all_clause opt_target_list
            into_clause from_clause where_clause
            group_clause having_clause window_clause
                {
                    SelectStmt *n = makeNode(SelectStmt);
                    n->targetList = $3;
                    n->intoClause = $4;
                    n->fromClause = $5;
                    n->whereClause = $6;
                    n->groupClause = ($7)->list;
                    n->groupDistinct = ($7)->distinct;
                    n->havingClause = $8;
                    n->windowClause = $9;
                    $$ = (Node *) n;
                }

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 */
    bool        groupDistinct;  /* Is this GROUP BY DISTINCT? */
    Node       *havingClause;   /* HAVING conditional-expression */
    List       *windowClause;   /* WINDOW window_name AS (...), ... */

    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 */
    LimitOption limitOption;    /* limit type */
    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 */
} SelectStmt;

select a, b from tb where a = 2; ----------> gram.y(bison)----------> struct SelectStmt

simple_select
    SELECT opt_all_clause opt_target_list /* optional */
    into_clause from_clause where_clause
    group_clause having_clause window_clause
        {
            SelectStmt *n = makeNode(SelectStmt);
            n->targetList = $3;
            n->intoClause = $4;
            n->fromClause = $5;
            n->whereClause = $6;
            n->groupClause = ($7)->list;
            n->groupDistinct = ($7)->distinct;
            n->havingClause = $8;
            n->windowClause = $9;
            $$ = (Node *) n;
        }

NB: opt_tartget_list is optional!!!

select a from tb;
select all a, b from tb;
select from tb;

涉及的其他子句：from_clause, opt_target_list, where_clause, ...