Implement feature of new FE/BE protocol whereby RowDescription identifies

[postgresql] / src / include / nodes / primnodes.h

/*-------------------------------------------------------------------------
 *
 * primnodes.h
 *        Definitions for "primitive" node types, those that are used in more
 *        than one of the parse/plan/execute stages of the query pipeline.
 *        Currently, these are mostly nodes for executable expressions
 *        and join trees.
 *
 *
 * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $Id: primnodes.h,v 1.82 2003/05/06 00:20:33 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef PRIMNODES_H
#define PRIMNODES_H

#include "access/attnum.h"
#include "nodes/pg_list.h"


/* ----------------------------------------------------------------
 *                                              node definitions
 * ----------------------------------------------------------------
 */

/*--------------------
 * Resdom (Result Domain)
 *
 * Notes:
 *
 * resno will normally be equal to the item's position in a targetlist,
 * but the code generally tries to avoid relying on that (eg, we avoid
 * using "nth()" rather than a search to find an item by resno).
 *
 * resname will be null if no name can easily be assigned to the column.
 * But it should never be null for user-visible columns (i.e., non-junk
 * columns in a toplevel targetlist).
 *
 * ressortgroupref is used in the representation of ORDER BY and
 * GROUP BY items.      Targetlist entries with ressortgroupref=0 are not
 * sort/group items.  If ressortgroupref>0, then this item is an ORDER BY or
 * GROUP BY 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 SortClause or GroupClause 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.
 *--------------------
 */
typedef struct Resdom
{
        NodeTag         type;
        AttrNumber      resno;                  /* attribute number (1..N) */
        Oid                     restype;                /* type of the value */
        int32           restypmod;              /* type-specific modifier of the value */
        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 */
} Resdom;


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

typedef enum InhOption
{
        INH_NO,                                         /* Do NOT scan child tables */
        INH_YES,                                        /* DO scan child tables */
        INH_DEFAULT                                     /* Use current SQL_inheritance option */
} InhOption;

/*
 * RangeVar - range variable, used in FROM clauses
 *
 * Also used to represent table names in utility statements; there, the alias
 * field is not used, and inhOpt shows 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 */
        InhOption       inhOpt;                 /* expand rel by inheritance? recursively
                                                                 * act on children? */
        bool            istemp;                 /* is this a temp relation/sequence? */
        Alias      *alias;                      /* table alias & optional column aliases */
} RangeVar;


/* ----------------------------------------------------------------
 *                                      node types for executable expressions
 * ----------------------------------------------------------------
 */

/*
 * Expr - generic superclass for executable-expression nodes
 *
 * All node types that are used in executable expression trees should derive
 * from Expr (that is, have Expr as their first field).  Since Expr only
 * contains NodeTag, this is a formality, but it is an easy form of
 * documentation.  See also the ExprState node types in execnodes.h.
 */
typedef struct Expr
{
        NodeTag         type;
} Expr;

/*
 * Var - expression node representing a variable (ie, a table column)
 *
 * Note: during parsing/planning, varnoold/varoattno are always just copies
 * of varno/varattno.  At the tail end of planning, Var nodes appearing in
 * upper-level plan nodes are reassigned to point to the outputs of their
 * subplans; for example, in a join node varno becomes INNER or OUTER and
 * varattno becomes the index of the proper element of that subplan's target
 * list.  But varnoold/varoattno continue to hold the original values.
 * The code doesn't really need varnoold/varoattno, but they are very useful
 * for debugging and interpreting completed plans, so we keep them around.
 */
#define    INNER                65000
#define    OUTER                65001

#define    PRS2_OLD_VARNO                       1
#define    PRS2_NEW_VARNO                       2

typedef struct Var
{
        Expr            xpr;
        Index           varno;                  /* index of this var's relation in the
                                                                 * range table (could also be INNER or
                                                                 * OUTER) */
        AttrNumber      varattno;               /* attribute number of this var, or zero
                                                                 * for all */
        Oid                     vartype;                /* pg_type tuple OID for the type of this
                                                                 * var */
        int32           vartypmod;              /* pg_attribute typmod value */
        Index           varlevelsup;

        /*
         * for subquery variables referencing outer relations; 0 in a normal
         * var, >0 means N levels up
         */
        Index           varnoold;               /* original value of varno, for debugging */
        AttrNumber      varoattno;              /* original value of varattno */
} Var;

/*
 * Const
 */
typedef struct Const
{
        Expr            xpr;
        Oid                     consttype;              /* PG_TYPE OID of the constant's datatype */
        int                     constlen;               /* typlen of the constant's datatype */
        Datum           constvalue;             /* the constant's value */
        bool            constisnull;    /* whether the constant is null (if true,
                                                                 * constvalue is undefined) */
        bool            constbyval;             /* whether this datatype is passed by value.
                                                                 * If true, then all the information is
                                                                 * stored in the Datum.
                                                                 * If false, then the Datum contains a
                                                                 * pointer to the information. */
} Const;

/* ----------------
 * Param
 *              paramkind - specifies the kind of parameter. The possible values
 *              for this field are specified in "params.h", and they are:
 *
 *              PARAM_NAMED: The parameter has a name, i.e. something
 *                              like `$.salary' or `$.foobar'.
 *                              In this case field `paramname' must be a valid name.
 *
 *              PARAM_NUM:       The parameter has only a numeric identifier,
 *                              i.e. something like `$1', `$2' etc.
 *                              The number is contained in the `paramid' field.
 *
 *              PARAM_EXEC:      The parameter is an internal executor parameter.
 *                              It has a number contained in the `paramid' field.
 * ----------------
 */
typedef struct Param
{
        Expr            xpr;
        int                     paramkind;              /* kind of parameter. See above */
        AttrNumber      paramid;                /* numeric ID for parameter ("$1") */
        char       *paramname;          /* name for parameter ("$.foo") */
        Oid                     paramtype;              /* PG_TYPE OID of parameter's datatype */
} Param;

/*
 * Aggref
 */
typedef struct Aggref
{
        Expr            xpr;
        Oid                     aggfnoid;               /* pg_proc Oid of the aggregate */
        Oid                     aggtype;                /* type Oid of result of the aggregate */
        Expr       *target;                     /* expression we are aggregating on */
        bool            aggstar;                /* TRUE if argument was really '*' */
        bool            aggdistinct;    /* TRUE if it's agg(DISTINCT ...) */
} Aggref;

/* ----------------
 *      ArrayRef: describes an array subscripting operation
 *
 * An ArrayRef can describe fetching a single element from an array,
 * fetching a subarray (array slice), storing a single element into
 * an array, or storing a slice.  The "store" cases work with an
 * initial array value and a source value that is inserted into the
 * appropriate part of the array; the result of the operation is an
 * entire new modified array value.
 *
 * If reflowerindexpr = NIL, then we are fetching or storing a single array
 * element at the subscripts given by refupperindexpr.  Otherwise we are
 * fetching or storing an array slice, that is a rectangular subarray
 * with lower and upper bounds given by the index expressions.
 * reflowerindexpr must be the same length as refupperindexpr when it
 * is not NIL.
 *
 * Note: refrestype is NOT the element type, but the array type,
 * when doing subarray fetch or either type of store.
 * ----------------
 */
typedef struct ArrayRef
{
        Expr            xpr;
        Oid                     refrestype;             /* type of the result of the ArrayRef
                                                                 * operation */
        Oid                     refarraytype;   /* type of the array proper */
        Oid                     refelemtype;    /* type of the array elements */
        List       *refupperindexpr;/* expressions that evaluate to upper
                                                                 * array indexes */
        List       *reflowerindexpr;/* expressions that evaluate to lower
                                                                 * array indexes */
        Expr       *refexpr;            /* the expression that evaluates to an
                                                                 * array value */
        Expr       *refassgnexpr;       /* expression for the source value, or
                                                                 * NULL if fetch */
} ArrayRef;

/*
 * CoercionContext - distinguishes the allowed set of type casts
 *
 * NB: ordering of the alternatives is significant; later (larger) values
 * allow more casts than earlier ones.
 */
typedef enum CoercionContext
{
        COERCION_IMPLICIT,                      /* coercion in context of expression */
        COERCION_ASSIGNMENT,            /* coercion in context of assignment */
        COERCION_EXPLICIT                       /* explicit cast operation */
} CoercionContext;

/*
 * CoercionForm - information showing how to display a function-call node
 */
typedef enum CoercionForm
{
        COERCE_EXPLICIT_CALL,           /* display as a function call */
        COERCE_EXPLICIT_CAST,           /* display as an explicit cast */
        COERCE_IMPLICIT_CAST,           /* implicit cast, so hide it */
        COERCE_DONTCARE                         /* special case for pathkeys */
} CoercionForm;

/*
 * FuncExpr - expression node for a function call
 */
typedef struct FuncExpr
{
        Expr            xpr;
        Oid                     funcid;                 /* PG_PROC OID of the function */
        Oid                     funcresulttype; /* PG_TYPE OID of result value */
        bool            funcretset;             /* true if function returns set */
        CoercionForm funcformat;        /* how to display this function call */
        List       *args;                       /* arguments to the function */
} FuncExpr;

/*
 * 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 is typically 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 */
        List       *args;                       /* arguments to the operator (1 or 2) */
} OpExpr;

/*
 * DistinctExpr - expression node for "x IS DISTINCT FROM y"
 *
 * Except for the nodetag, this is represented identically to an OpExpr
 * referencing the "=" operator for x and y.
 * We use "=", not the more obvious "<>", because more datatypes have "="
 * than "<>".  This means the executor must invert the operator result.
 * Note that the operator function won't be called at all if either input
 * is NULL, since then the result can be determined directly.
 */
typedef OpExpr DistinctExpr;

/*
 * BoolExpr - expression node for the basic Boolean operators AND, OR, NOT
 *
 * Notice the arguments are given as a List.  For NOT, of course the list
 * must always have exactly one element.  For AND and OR, the executor can
 * handle any number of arguments.  The parser treats AND and OR as binary
 * and so it only produces two-element lists, but the optimizer will flatten
 * trees of AND and OR nodes to produce longer lists when possible.
 */
typedef enum BoolExprType
{
        AND_EXPR, OR_EXPR, NOT_EXPR
} BoolExprType;

typedef struct BoolExpr
{
        Expr            xpr;
        BoolExprType boolop;
        List       *args;                       /* arguments to this expression */
} BoolExpr;

/* ----------------
 * SubLink
 *
 * A SubLink represents a subselect appearing in an expression, and in some
 * cases also the combining operator(s) just above it.  The subLinkType
 * indicates the form of the expression represented:
 *      EXISTS_SUBLINK          EXISTS(SELECT ...)
 *      ALL_SUBLINK                     (lefthand) op ALL (SELECT ...)
 *      ANY_SUBLINK                     (lefthand) op ANY (SELECT ...)
 *      MULTIEXPR_SUBLINK       (lefthand) op (SELECT ...)
 *      EXPR_SUBLINK            (SELECT with single targetlist item ...)
 *      ARRAY_SUBLINK           ARRAY(SELECT with single targetlist item ...)
 * For ALL, ANY, and MULTIEXPR, the lefthand is a list of expressions of the
 * same length as the subselect's targetlist.  MULTIEXPR will *always* have
 * a list with more than one entry; if the subselect has just one target
 * then the parser will create an EXPR_SUBLINK instead (and any operator
 * above the subselect will be represented separately).  Note that both
 * MULTIEXPR and EXPR require the subselect to deliver only one row.
 * ARRAY requires just one target column, and creates an array of the target
 * column's type using one or more rows resulting from the subselect.
 * ALL, ANY, and MULTIEXPR require the combining operators to deliver boolean
 * results.  These are reduced to one result per row using OR or AND semantics
 * depending on the "useOr" flag.  ALL and ANY combine the per-row results
 * using AND and OR semantics respectively.
 *
 * SubLink is classed as an Expr node, but it is not actually executable;
 * it must be replaced in the expression tree by a SubPlan node during
 * planning.
 *
 * NOTE: in the raw output of gram.y, lefthand contains a list of raw
 * expressions; useOr and operOids are not filled in yet.  Also, subselect
 * is a raw parsetree.  During parse analysis, the parser transforms the
 * lefthand expression list using normal expression transformation rules.
 * It fills operOids with the OIDs representing the specific operator(s)
 * to apply to each pair of lefthand and targetlist expressions.
 * And subselect is transformed to a Query.  This is the representation
 * seen in saved rules and in the rewriter.
 *
 * In EXISTS, EXPR, and ARRAY SubLinks, lefthand, operName, and operOids are
 * unused and are always NIL.  useOr is not significant either for these
 * sublink types.
 * ----------------
 */
typedef enum SubLinkType
{
        EXISTS_SUBLINK,
        ALL_SUBLINK,
        ANY_SUBLINK,
        MULTIEXPR_SUBLINK,
        EXPR_SUBLINK,
        ARRAY_SUBLINK
} SubLinkType;


typedef struct SubLink
{
        Expr            xpr;
        SubLinkType subLinkType;        /* EXISTS, ALL, ANY, MULTIEXPR, EXPR */
        bool            useOr;                  /* TRUE to combine column results with
                                                                 * "OR" not "AND" */
        List       *lefthand;           /* list of outer-query expressions on the
                                                                 * left */
        List       *operName;           /* originally specified operator name */
        List       *operOids;           /* OIDs of actual combining operators */
        Node       *subselect;          /* subselect as Query* or parsetree */
} SubLink;

/*
 * SubPlan - executable expression node for a subplan (sub-SELECT)
 *
 * The planner replaces SubLink nodes in expression trees with SubPlan
 * nodes after it has finished planning the subquery.  SubPlan contains
 * a sub-plantree and rtable instead of a sub-Query.
 *
 * In an ordinary subplan, "exprs" points to a list of executable expressions
 * (OpExpr trees) for the combining operators; their left-hand arguments are
 * the original lefthand expressions, and their right-hand arguments are
 * PARAM_EXEC Param nodes representing the outputs of the sub-select.
 * (NOTE: runtime coercion functions may be inserted as well.)  But if the
 * sub-select becomes an initplan rather than a subplan, these executable
 * expressions are part of the outer plan's expression tree (and the SubPlan
 * node itself is not).  In this case "exprs" is NIL to avoid duplication.
 *
 * The planner also derives lists of the values that need to be passed into
 * and out of the subplan.  Input values are represented as a list "args" of
 * expressions to be evaluated in the outer-query context (currently these
 * args are always just Vars, but in principle they could be any expression).
 * The values are assigned to the global PARAM_EXEC params indexed by parParam
 * (the parParam and args lists must have the same ordering).  setParam is a
 * list of the PARAM_EXEC params that are computed by the sub-select, if it
 * is an initplan; they are listed in order by sub-select output column
 * position.  (parParam and setParam are integer Lists, not Bitmapsets,
 * because their ordering is significant.)
 */
typedef struct SubPlan
{
        Expr            xpr;
        /* Fields copied from original SubLink: */
        SubLinkType subLinkType;        /* EXISTS, ALL, ANY, MULTIEXPR, EXPR */
        bool            useOr;                  /* TRUE to combine column results with
                                                                 * "OR" not "AND" */
        /* The combining operators, transformed to executable expressions: */
        List       *exprs;                      /* list of OpExpr expression trees */
        List       *paramIds;           /* IDs of Params embedded in the above */
        /* Note: paramIds has a one-to-one correspondence to the exprs list */
        /* The subselect, transformed to a Plan: */
        struct Plan *plan;                      /* subselect plan itself */
        int                     plan_id;                /* dummy thing because of we haven't equal
                                                                 * funcs for plan nodes... actually, we
                                                                 * could put *plan itself somewhere else
                                                                 * (TopPlan node ?)... */
        List       *rtable;                     /* range table for subselect */
        /* Information about execution strategy: */
        bool            useHashTable;   /* TRUE to store subselect output in a hash
                                                                 * table (implies we are doing "IN") */
        bool            unknownEqFalse; /* TRUE if it's okay to return FALSE when
                                                                 * the spec result is UNKNOWN; this allows
                                                                 * much simpler handling of null values */
        /* Information for passing params into and out of the subselect: */
        /* setParam and parParam are lists of integers (param IDs) */
        List       *setParam;           /* initplan subqueries have to set these
                                                                 * Params for parent plan */
        List       *parParam;           /* indices of input Params from parent plan */
        List       *args;                       /* exprs to pass as parParam values */
} SubPlan;

/* ----------------
 * FieldSelect
 *
 * FieldSelect represents the operation of extracting one field from a tuple
 * value.  At runtime, the input expression is expected to yield a Datum
 * that contains a pointer-to-TupleTableSlot.  The specified field number
 * is extracted and returned as a Datum.
 * ----------------
 */

typedef struct FieldSelect
{
        Expr            xpr;
        Expr       *arg;                        /* input expression */
        AttrNumber      fieldnum;               /* attribute number of field to extract */
        Oid                     resulttype;             /* type of the field (result type of this
                                                                 * node) */
        int32           resulttypmod;   /* output typmod (usually -1) */
} FieldSelect;

/* ----------------
 * RelabelType
 *
 * RelabelType represents a "dummy" type coercion between two binary-
 * compatible datatypes, such as reinterpreting the result of an OID
 * expression as an int4.  It is a no-op at runtime; we only need it
 * to provide a place to store the correct type to be attributed to
 * the expression result during type resolution.  (We can't get away
 * with just overwriting the type field of the input expression node,
 * so we need a separate node to show the coercion's result type.)
 * ----------------
 */

typedef struct RelabelType
{
        Expr            xpr;
        Expr       *arg;                        /* input expression */
        Oid                     resulttype;             /* output type of coercion expression */
        int32           resulttypmod;   /* output typmod (usually -1) */
        CoercionForm relabelformat;     /* how to display this node */
} RelabelType;

/*
 * CaseExpr - a CASE expression
 */
typedef struct CaseExpr
{
        Expr            xpr;
        Oid                     casetype;               /* type of expression result */
        Expr       *arg;                        /* implicit equality comparison argument */
        List       *args;                       /* the arguments (list of WHEN clauses) */
        Expr       *defresult;          /* the default result (ELSE clause) */
} CaseExpr;

/*
 * CaseWhen - an argument to a CASE expression
 */
typedef struct CaseWhen
{
        Expr            xpr;
        Expr       *expr;                       /* condition expression */
        Expr       *result;                     /* substitution result */
} CaseWhen;

/*
 * ArrayExpr - an ARRAY[] expression
 *
 * Note: if ndims > 1, then the array elements are all ArrayExprs of the
 * same type and ndims one less.
 */
typedef struct ArrayExpr
{
        Expr            xpr;
        Oid                     array_typeid;   /* type of expression result */
        Oid                     element_typeid; /* common type of expression elements */
        List       *elements;           /* the array elements */
        int                     ndims;                  /* number of array dimensions */
} ArrayExpr;

/*
 * CoalesceExpr - a COALESCE expression
 */
typedef struct CoalesceExpr
{
        Expr    xpr;
        Oid             coalescetype;           /* type of expression result */
        List   *args;                           /* the arguments */
} CoalesceExpr;

/*
 * NullIfExpr - a NULLIF expression
 *
 * Like DistinctExpr, this is represented the same as an OpExpr referencing
 * the "=" operator for x and y.
 */
typedef OpExpr NullIfExpr;

/* ----------------
 * NullTest
 *
 * NullTest represents the operation of testing a value for NULLness.
 * Currently, we only support scalar input values, but eventually a
 * row-constructor input should be supported.
 * The appropriate test is performed and returned as a boolean Datum.
 * ----------------
 */

typedef enum NullTestType
{
        IS_NULL, IS_NOT_NULL
} NullTestType;

typedef struct NullTest
{
        Expr            xpr;
        Expr       *arg;                        /* input expression */
        NullTestType nulltesttype;      /* IS NULL, IS NOT NULL */
} NullTest;

/*
 * BooleanTest
 *
 * BooleanTest represents the operation of determining whether a boolean
 * is TRUE, FALSE, or UNKNOWN (ie, NULL).  All six meaningful combinations
 * are supported.  Note that a NULL input does *not* cause a NULL result.
 * The appropriate test is performed and returned as a boolean Datum.
 */

typedef enum BoolTestType
{
        IS_TRUE, IS_NOT_TRUE, IS_FALSE, IS_NOT_FALSE, IS_UNKNOWN, IS_NOT_UNKNOWN
} BoolTestType;

typedef struct BooleanTest
{
        Expr            xpr;
        Expr       *arg;                        /* input expression */
        BoolTestType booltesttype;      /* test type */
} BooleanTest;

/*
 * CoerceToDomain
 *
 * CoerceToDomain represents the operation of coercing a value to a domain
 * type.  At runtime (and not before) the precise set of constraints to be
 * checked will be determined.  If the value passes, it is returned as the
 * result; if not, an error is raised.  Note that this is equivalent to
 * RelabelType in the scenario where no constraints are applied.
 */
typedef struct CoerceToDomain
{
        Expr            xpr;
        Expr       *arg;                        /* input expression */
        Oid                     resulttype;             /* domain type ID (result type) */
        int32           resulttypmod;   /* output typmod (currently always -1) */
        CoercionForm coercionformat; /* how to display this node */
} CoerceToDomain;

/*
 * Placeholder node for the value to be processed by a domain's check
 * constraint.  This is effectively like a Param, but can be implemented more
 * simply since we need only one replacement value at a time.
 *
 * Note: the typeId/typeMod will be set from the domain's base type, not
 * the domain itself.  This is because we shouldn't consider the value to
 * be a member of the domain if we haven't yet checked its constraints.
 */
typedef struct CoerceToDomainValue
{
        Expr            xpr;
        Oid                     typeId;                 /* type for substituted value */
        int32           typeMod;                /* typemod for substituted value */
} CoerceToDomainValue;


/*
 * 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.
 *
 * The separation between TargetEntry and Resdom is historical.  One of these
 * days, Resdom should probably get folded into TargetEntry.
 */
typedef struct TargetEntry
{
        Expr            xpr;
        Resdom     *resdom;                     /* descriptor for targetlist item */
        Expr       *expr;                       /* expression to evaluate */
} TargetEntry;


/* ----------------------------------------------------------------
 *                                      node types for join trees
 *
 * The leaves of a join tree structure are RangeTblRef nodes.  Above
 * these, JoinExpr nodes can appear to denote a specific kind of join
 * or qualified join.  Also, FromExpr nodes can appear to denote an
 * ordinary cross-product join ("FROM foo, bar, baz WHERE ...").
 * FromExpr is like a JoinExpr of jointype JOIN_INNER, except that it
 * may have any number of child nodes, not just two.  Also, there is an
 * implementation-defined difference: the planner is allowed to join the
 * children of a FromExpr using whatever join order seems good to it.
 * At present, JoinExpr nodes are always joined in exactly the order
 * implied by the jointree structure (except the planner may choose to
 * swap inner and outer members of a join pair).
 *
 * NOTE: the top level of a Query's jointree is always a FromExpr.
 * Even if the jointree contains no rels, there will be a FromExpr.
 *
 * NOTE: the qualification expressions present in JoinExpr nodes are
 * *in addition to* the query's main WHERE clause, which appears as the
 * qual of the top-level FromExpr.      The reason for associating quals with
 * specific nodes in the jointree is that the position of a qual is critical
 * when outer joins are present.  (If we enforce a qual too soon or too late,
 * that may cause the outer join to produce the wrong set of NULL-extended
 * rows.)  If all joins are inner joins then all the qual positions are
 * semantically interchangeable.
 *
 * NOTE: in the raw output of gram.y, a join tree contains RangeVar,
 * RangeSubselect, and RangeFunction nodes, which are all replaced by
 * RangeTblRef nodes during the parse analysis phase.  Also, the top-level
 * FromExpr is added during parse analysis; the grammar regards FROM and
 * WHERE as separate.
 * ----------------------------------------------------------------
 */

/*
 * 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, using, 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.
 *----------
 */
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       *using;                      /* 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 */
} 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;

#endif   /* PRIMNODES_H */