primnodes.h

来自「PostgreSQL7.4.6 for Linux」· C头文件 代码 · 共 832 行 · 第 1/3 页

{
	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 multidims is false, the constituent expressions all yield the
 * scalar type identified by element_typeid.  If multidims is true, the
 * constituent expressions all yield arrays of element_typeid (ie, the same
 * type as array_typeid); at runtime we must check for compatible subscripts.
 */
typedef struct ArrayExpr
{
	Expr		xpr;
	Oid			array_typeid;	/* type of expression result */
	Oid			element_typeid; /* common type of array elements */
	List	   *elements;		/* the array elements or sub-arrays */
	bool		multidims;		/* true if elements are sub-arrays */
} 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;

/*
 * Placeholder node for a DEFAULT marker in an INSERT or UPDATE command.
 *
 * This is not an executable expression: it must be replaced by the actual
 * column default expression during rewriting.	But it is convenient to
 * treat it as an expression node during parsing and rewriting.
 */
typedef struct SetToDefault
{
	Expr		xpr;
	Oid			typeId;			/* type for substituted value */
	int32		typeMod;		/* typemod for substituted value */
} SetToDefault;

/*
 * 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 */