Unverified 提交 4f23bb18 authored 作者: Evgenij Ryazanov's avatar Evgenij Ryazanov 提交者: GitHub

Merge pull request #1456 from katzyn/window

Add experimental implementation of remaining types of window frames
......@@ -2550,11 +2550,8 @@ They also may require a lot of memory for large queries.
"
"Other Grammar","Window frame","
[RANGE BETWEEN {
UNBOUNDED PRECEDING AND CURRENT ROW
|CURRENT ROW AND UNBOUNDED FOLLOWING
|UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
}]
ROWS|RANGE|GROUP
{windowFramePreceding|BETWEEN windowFrameBound AND windowFrameBound}
[EXCLUDE {CURRENT ROW|GROUP|TIES|NO OTHERS}]
","
A window frame clause.
......@@ -2563,6 +2560,30 @@ Is currently supported only in aggregates and FIRST_VALUE(), LAST_VALUE(), and N
RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW EXCLUDE GROUP
"
"Other Grammar","Window frame preceding","
UNBOUNDED PRECEDING|value PRECEDING|CURRENT ROW
","
A window frame preceding clause.
If value is specified it should be non-negative value or parameter.
","
UNBOUNDED PRECEDING
1 PRECEDING
CURRENT ROW
"
"Other Grammar","Window frame bound","
UNBOUNDED PRECEDING|value PRECEDING|CURRENT ROW
|value FOLLOWING|UNBOUNDED FOLLOWING
","
A window frame bound clause.
If value is specified it should be non-negative value or parameter.
","
UNBOUNDED PRECEDING
UNBOUNDED FOLLOWING
1 FOLLOWING
CURRENT ROW
"
"Other Grammar","Term","
value
| columnName
......
......@@ -176,8 +176,10 @@ import org.h2.expression.aggregate.Aggregate.AggregateType;
import org.h2.expression.aggregate.JavaAggregate;
import org.h2.expression.aggregate.Window;
import org.h2.expression.aggregate.WindowFrame;
import org.h2.expression.aggregate.WindowFrame.SimpleExtent;
import org.h2.expression.aggregate.WindowFrame.WindowFrameExclusion;
import org.h2.expression.aggregate.WindowFrameBound;
import org.h2.expression.aggregate.WindowFrameBoundType;
import org.h2.expression.aggregate.WindowFrameExclusion;
import org.h2.expression.aggregate.WindowFrameUnits;
import org.h2.expression.aggregate.WindowFunction;
import org.h2.expression.aggregate.WindowFunction.WindowFunctionType;
import org.h2.index.Index;
......@@ -3074,8 +3076,7 @@ public class Parser {
frame = readWindowFrame();
break;
default:
frame = new WindowFrame(SimpleExtent.RANGE_BETWEEN_UNBOUNDED_PRECEDING_AND_CURRENT_ROW,
WindowFrameExclusion.EXCLUDE_NO_OTHERS);
frame = null;
}
} else {
frame = readWindowFrame();
......@@ -3092,29 +3093,27 @@ public class Parser {
}
private WindowFrame readWindowFrame() {
SimpleExtent extent;
WindowFrameExclusion exclusion = WindowFrameExclusion.EXCLUDE_NO_OTHERS;
if (readIf("RANGE")) {
read("BETWEEN");
if (readIf("UNBOUNDED")) {
read("PRECEDING");
read("AND");
if (readIf("CURRENT")) {
read("ROW");
extent = SimpleExtent.RANGE_BETWEEN_UNBOUNDED_PRECEDING_AND_CURRENT_ROW;
WindowFrameUnits units;
if (readIf("ROWS")) {
units = WindowFrameUnits.ROWS;
} else if (readIf("RANGE")) {
units = WindowFrameUnits.RANGE;
} else if (readIf("GROUPS")) {
units = WindowFrameUnits.GROUPS;
} else {
read("UNBOUNDED");
read("FOLLOWING");
extent = SimpleExtent.RANGE_BETWEEN_UNBOUNDED_PRECEDING_AND_UNBOUNDED_FOLLOWING;
return null;
}
} else {
read("CURRENT");
read("ROW");
WindowFrameBound starting, following;
if (readIf("BETWEEN")) {
starting = readWindowFrameRange();
read("AND");
read("UNBOUNDED");
read("FOLLOWING");
extent = SimpleExtent.RANGE_BETWEEN_CURRENT_ROW_AND_UNBOUNDED_FOLLOWING;
following = readWindowFrameRange();
} else {
starting = readWindowFrameStarting();
following = null;
}
int idx = lastParseIndex;
WindowFrameExclusion exclusion = WindowFrameExclusion.EXCLUDE_NO_OTHERS;
if (readIf("EXCLUDE")) {
if (readIf("CURRENT")) {
read("ROW");
......@@ -3128,10 +3127,55 @@ public class Parser {
read("OTHERS");
}
}
} else {
extent = SimpleExtent.RANGE_BETWEEN_UNBOUNDED_PRECEDING_AND_CURRENT_ROW;
WindowFrame frame = new WindowFrame(units, starting, following, exclusion);
if (!frame.isValid()) {
throw DbException.getSyntaxError(sqlCommand, idx);
}
return frame;
}
private WindowFrameBound readWindowFrameStarting() {
if (readIf("UNBOUNDED")) {
read("PRECEDING");
return new WindowFrameBound(WindowFrameBoundType.UNBOUNDED_PRECEDING, null);
}
if (readIf("CURRENT")) {
read("ROW");
return new WindowFrameBound(WindowFrameBoundType.CURRENT_ROW, null);
}
Expression value = readValueOrParameter();
read("PRECEDING");
return new WindowFrameBound(WindowFrameBoundType.PRECEDING, value);
}
private WindowFrameBound readWindowFrameRange() {
if (readIf("UNBOUNDED")) {
if (readIf("PRECEDING")) {
return new WindowFrameBound(WindowFrameBoundType.UNBOUNDED_PRECEDING, null);
}
read("FOLLOWING");
return new WindowFrameBound(WindowFrameBoundType.UNBOUNDED_FOLLOWING, null);
}
if (readIf("CURRENT")) {
read("ROW");
return new WindowFrameBound(WindowFrameBoundType.CURRENT_ROW, null);
}
Expression value = readValueOrParameter();
if (readIf("PRECEDING")) {
return new WindowFrameBound(WindowFrameBoundType.PRECEDING, value);
}
read("FOLLOWING");
return new WindowFrameBound(WindowFrameBoundType.FOLLOWING, value);
}
private Expression readValueOrParameter() {
int index = parseIndex;
Expression value = readExpression();
if (!(value instanceof ValueExpression) && !(value instanceof Parameter)) {
parseIndex = index;
throw getSyntaxError();
}
return new WindowFrame(extent, exclusion);
return value;
}
private AggregateType getAggregateType(String name) {
......
......@@ -445,7 +445,7 @@ public abstract class AbstractAggregate extends Expression {
int size = ordered.size();
for (int i = 0; i < size; i++) {
Object aggregateData = createAggregateData();
for (Iterator<Value[]> iter = frame.iterator(ordered, getOverOrderBySort(), i, false); iter
for (Iterator<Value[]> iter = frame.iterator(session, ordered, getOverOrderBySort(), i, false); iter
.hasNext();) {
updateFromExpressions(session, aggregateData, iter.next());
}
......
......@@ -64,6 +64,11 @@ public final class Window {
public Window(ArrayList<Expression> partitionBy, ArrayList<SelectOrderBy> orderBy, WindowFrame frame) {
this.partitionBy = partitionBy;
this.orderBy = orderBy;
if (frame == null) {
frame = new WindowFrame(WindowFrameUnits.RANGE,
new WindowFrameBound(WindowFrameBoundType.UNBOUNDED_PRECEDING, null), null,
WindowFrameExclusion.EXCLUDE_NO_OTHERS);
}
this.frame = frame;
}
......
/*
* Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.expression.aggregate;
import org.h2.expression.Expression;
/**
* Window frame bound.
*/
public class WindowFrameBound {
private final WindowFrameBoundType type;
private final Expression value;
/**
* Creates new instance of window frame bound.
*
* @param type
* bound type
* @param value
* bound value, if any
*/
public WindowFrameBound(WindowFrameBoundType type, Expression value) {
this.type = type;
if (type == WindowFrameBoundType.PRECEDING || type == WindowFrameBoundType.FOLLOWING) {
this.value = value;
} else {
this.value = null;
}
}
/**
* Returns the type
*
* @return the type
*/
public WindowFrameBoundType getType() {
return type;
}
/**
* Returns the value.
*
* @return the value
*/
public Expression getValue() {
return value;
}
/**
* Returns SQL representation.
*
* @param following
* if false return SQL for starting clause, if true return SQL
* for following clause
* @return SQL representation.
* @see Expression#getSQL()
*/
public String getSQL(boolean following) {
if (type == WindowFrameBoundType.PRECEDING || type == WindowFrameBoundType.FOLLOWING) {
return value.getSQL() + ' ' + type.getSQL();
}
return type.getSQL();
}
}
/*
* Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.expression.aggregate;
/**
* Window frame bound type.
*/
public enum WindowFrameBoundType {
/**
* UNBOUNDED PRECEDING clause.
*/
UNBOUNDED_PRECEDING("UNBOUNDED PRECEDING"),
/**
* PRECEDING clause.
*/
PRECEDING("PRECEDING"),
/**
* CURRENT_ROW clause.
*/
CURRENT_ROW("CURRENT_ROW"),
/**
* FOLLOWING clause.
*/
FOLLOWING("FOLLOWING"),
/**
* UNBOUNDED FOLLOWING clause.
*/
UNBOUNDED_FOLLOWING("UNBOUNDED FOLLOWING");
private final String sql;
private WindowFrameBoundType(String sql) {
this.sql = sql;
}
/**
* Returns SQL representation.
*
* @return SQL representation.
* @see org.h2.expression.Expression#getSQL()
*/
public String getSQL() {
return sql;
}
}
/*
* Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.expression.aggregate;
/**
* Window frame exclusion clause.
*/
public enum WindowFrameExclusion {
/**
* EXCLUDE CURRENT ROW exclusion clause.
*/
EXCLUDE_CURRENT_ROW("EXCLUDE CURRENT ROW"),
/**
* EXCLUDE GROUP exclusion clause.
*/
EXCLUDE_GROUP("EXCLUDE GROUP"),
/**
* EXCLUDE TIES exclusion clause.
*/
EXCLUDE_TIES("EXCLUDE TIES"),
/**
* EXCLUDE NO OTHERS exclusion clause.
*/
EXCLUDE_NO_OTHERS("EXCLUDE NO OTHERS"),
;
private final String sql;
private WindowFrameExclusion(String sql) {
this.sql = sql;
}
/**
* Returns SQL representation.
*
* @return SQL representation.
* @see org.h2.expression.Expression#getSQL()
*/
public String getSQL() {
return sql;
}
}
/*
* Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.expression.aggregate;
/**
* Window frame units.
*/
public enum WindowFrameUnits {
/**
* ROWS unit.
*/
ROWS,
/**
* RANGE unit.
*/
RANGE,
/**
* GROUPS unit.
*/
GROUPS,
;
/**
* Returns SQL representation.
*
* @return SQL representation.
* @see org.h2.expression.Expression#getSQL()
*/
public String getSQL() {
return name();
}
}
......@@ -321,11 +321,11 @@ public class WindowFunction extends AbstractAggregate {
Value v;
switch (type) {
case FIRST_VALUE: {
v = getNthValue(frame.iterator(ordered, getOverOrderBySort(), i, false), 0, ignoreNulls);
v = getNthValue(frame.iterator(session, ordered, getOverOrderBySort(), i, false), 0, ignoreNulls);
break;
}
case LAST_VALUE:
v = getNthValue(frame.iterator(ordered, getOverOrderBySort(), i, true), 0, ignoreNulls);
v = getNthValue(frame.iterator(session, ordered, getOverOrderBySort(), i, true), 0, ignoreNulls);
break;
case NTH_VALUE: {
int n = row[1].getInt();
......@@ -333,7 +333,7 @@ public class WindowFunction extends AbstractAggregate {
throw DbException.getInvalidValueException("nth row", n);
}
n--;
Iterator<Value[]> iter = frame.iterator(ordered, getOverOrderBySort(), i, fromLast);
Iterator<Value[]> iter = frame.iterator(session, ordered, getOverOrderBySort(), i, fromLast);
v = getNthValue(iter, n, ignoreNulls);
break;
}
......
......@@ -275,3 +275,160 @@ SELECT
DROP TABLE TEST;
> ok
CREATE TABLE TEST(ID INT, VALUE INT);
> ok
INSERT INTO TEST VALUES
(1, 1),
(2, 1),
(3, 5),
(4, 8),
(5, 8),
(6, 8),
(7, 9),
(8, 9);
> update count: 8
SELECT *,
ARRAY_AGG(ID) OVER (ORDER BY VALUE ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING) R_ID,
ARRAY_AGG(VALUE) OVER (ORDER BY VALUE ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING) R_V,
ARRAY_AGG(ID) OVER (ORDER BY VALUE RANGE BETWEEN 1 PRECEDING AND 1 FOLLOWING) V_ID,
ARRAY_AGG(VALUE) OVER (ORDER BY VALUE RANGE BETWEEN 1 PRECEDING AND 1 FOLLOWING) V_V,
ARRAY_AGG(VALUE) OVER (ORDER BY VALUE DESC RANGE BETWEEN 1 PRECEDING AND 1 FOLLOWING) V_V_R,
ARRAY_AGG(ID) OVER (ORDER BY VALUE GROUPS BETWEEN 1 PRECEDING AND 1 FOLLOWING) G_ID,
ARRAY_AGG(VALUE) OVER (ORDER BY VALUE GROUPS BETWEEN 1 PRECEDING AND 1 FOLLOWING) G_V
FROM TEST;
> ID VALUE R_ID R_V V_ID V_V V_V_R G_ID G_V
> -- ----- --------- --------- --------------- --------------- --------------- ------------------ ------------------
> 1 1 (1, 2) (1, 1) (1, 2) (1, 1) (1, 1) (1, 2, 3) (1, 1, 5)
> 2 1 (1, 2, 3) (1, 1, 5) (1, 2) (1, 1) (1, 1) (1, 2, 3) (1, 1, 5)
> 3 5 (2, 3, 4) (1, 5, 8) (3) (5) (5) (1, 2, 3, 4, 5, 6) (1, 1, 5, 8, 8, 8)
> 4 8 (3, 4, 5) (5, 8, 8) (4, 5, 6, 7, 8) (8, 8, 8, 9, 9) (9, 9, 8, 8, 8) (3, 4, 5, 6, 7, 8) (5, 8, 8, 8, 9, 9)
> 5 8 (4, 5, 6) (8, 8, 8) (4, 5, 6, 7, 8) (8, 8, 8, 9, 9) (9, 9, 8, 8, 8) (3, 4, 5, 6, 7, 8) (5, 8, 8, 8, 9, 9)
> 6 8 (5, 6, 7) (8, 8, 9) (4, 5, 6, 7, 8) (8, 8, 8, 9, 9) (9, 9, 8, 8, 8) (3, 4, 5, 6, 7, 8) (5, 8, 8, 8, 9, 9)
> 7 9 (6, 7, 8) (8, 9, 9) (4, 5, 6, 7, 8) (8, 8, 8, 9, 9) (9, 9, 8, 8, 8) (4, 5, 6, 7, 8) (8, 8, 8, 9, 9)
> 8 9 (7, 8) (9, 9) (4, 5, 6, 7, 8) (8, 8, 8, 9, 9) (9, 9, 8, 8, 8) (4, 5, 6, 7, 8) (8, 8, 8, 9, 9)
> rows (ordered): 8
SELECT *, ARRAY_AGG(ID) OVER (ORDER BY VALUE ROWS -1 PRECEDING) FROM TEST;
> exception INVALID_VALUE_2
SELECT *, ARRAY_AGG(ID) OVER (ORDER BY ID ROWS BETWEEN 2 PRECEDING AND 1 PRECEDING) FROM TEST FETCH FIRST 4 ROWS ONLY;
> ID VALUE ARRAY_AGG(ID) OVER (ORDER BY ID ROWS BETWEEN 2 PRECEDING AND 1 PRECEDING)
> -- ----- -------------------------------------------------------------------------
> 1 1 null
> 2 1 (1)
> 3 5 (1, 2)
> 4 8 (2, 3)
> rows (ordered): 4
SELECT *, ARRAY_AGG(ID) OVER (ORDER BY ID ROWS BETWEEN 1 FOLLOWING AND 2 FOLLOWING) FROM TEST OFFSET 4 ROWS;
> ID VALUE ARRAY_AGG(ID) OVER (ORDER BY ID ROWS BETWEEN 1 FOLLOWING AND 2 FOLLOWING)
> -- ----- -------------------------------------------------------------------------
> 5 8 (6, 7)
> 6 8 (7, 8)
> 7 9 (8)
> 8 9 null
> rows (ordered): 4
SELECT *, ARRAY_AGG(ID) OVER (ORDER BY ID RANGE BETWEEN 2 PRECEDING AND 1 PRECEDING) FROM TEST FETCH FIRST 4 ROWS ONLY;
> ID VALUE ARRAY_AGG(ID) OVER (ORDER BY ID RANGE BETWEEN 2 PRECEDING AND 1 PRECEDING)
> -- ----- --------------------------------------------------------------------------
> 1 1 null
> 2 1 (1)
> 3 5 (1, 2)
> 4 8 (2, 3)
> rows (ordered): 4
SELECT *, ARRAY_AGG(ID) OVER (ORDER BY ID RANGE BETWEEN 1 FOLLOWING AND 2 FOLLOWING) FROM TEST OFFSET 4 ROWS;
> ID VALUE ARRAY_AGG(ID) OVER (ORDER BY ID RANGE BETWEEN 1 FOLLOWING AND 2 FOLLOWING)
> -- ----- --------------------------------------------------------------------------
> 5 8 (6, 7)
> 6 8 (7, 8)
> 7 9 (8)
> 8 9 null
> rows (ordered): 4
SELECT *,
ARRAY_AGG(ID) OVER (ORDER BY VALUE GROUPS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING) U_P,
ARRAY_AGG(ID) OVER (ORDER BY VALUE GROUPS BETWEEN 2 PRECEDING AND 1 PRECEDING) P,
ARRAY_AGG(ID) OVER (ORDER BY VALUE GROUPS BETWEEN 1 FOLLOWING AND 2 FOLLOWING) F,
ARRAY_AGG(ID) OVER (ORDER BY VALUE GROUPS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING) U_F
FROM TEST;
> ID VALUE U_P P F U_F
> -- ----- ------------------ ------------ --------------- ------------------
> 1 1 null null (3, 4, 5, 6) (3, 4, 5, 6, 7, 8)
> 2 1 null null (3, 4, 5, 6) (3, 4, 5, 6, 7, 8)
> 3 5 (1, 2) (1, 2) (4, 5, 6, 7, 8) (4, 5, 6, 7, 8)
> 4 8 (1, 2, 3) (1, 2, 3) (7, 8) (7, 8)
> 5 8 (1, 2, 3) (1, 2, 3) (7, 8) (7, 8)
> 6 8 (1, 2, 3) (1, 2, 3) (7, 8) (7, 8)
> 7 9 (1, 2, 3, 4, 5, 6) (3, 4, 5, 6) null null
> 8 9 (1, 2, 3, 4, 5, 6) (3, 4, 5, 6) null null
> rows (ordered): 8
SELECT *,
ARRAY_AGG(ID) OVER (ORDER BY VALUE GROUPS BETWEEN 1 PRECEDING AND 0 PRECEDING) P,
ARRAY_AGG(ID) OVER (ORDER BY VALUE GROUPS BETWEEN 0 FOLLOWING AND 1 FOLLOWING) F
FROM TEST;
> ID VALUE P F
> -- ----- --------------- ---------------
> 1 1 (1, 2) (1, 2, 3)
> 2 1 (1, 2) (1, 2, 3)
> 3 5 (1, 2, 3) (3, 4, 5, 6)
> 4 8 (3, 4, 5, 6) (4, 5, 6, 7, 8)
> 5 8 (3, 4, 5, 6) (4, 5, 6, 7, 8)
> 6 8 (3, 4, 5, 6) (4, 5, 6, 7, 8)
> 7 9 (4, 5, 6, 7, 8) (7, 8)
> 8 9 (4, 5, 6, 7, 8) (7, 8)
> rows (ordered): 8
SELECT *, ARRAY_AGG(ID) OVER (ORDER BY ID RANGE BETWEEN CURRENT ROW AND 1 PRECEDING) FROM TEST;
> exception SYNTAX_ERROR_1
DROP TABLE TEST;
> ok
CREATE TABLE TEST (ID INT, VALUE INT);
> ok
INSERT INTO TEST VALUES
(1, 1),
(2, 1),
(3, 2),
(4, 2),
(5, 3),
(6, 3),
(7, 4),
(8, 4);
> update count: 8
SELECT *, ARRAY_AGG(ID) OVER (ORDER BY VALUE RANGE BETWEEN 2 PRECEDING AND 1 PRECEDING) FROM TEST;
> ID VALUE ARRAY_AGG(ID) OVER (ORDER BY VALUE RANGE BETWEEN 2 PRECEDING AND 1 PRECEDING)
> -- ----- -----------------------------------------------------------------------------
> 1 1 null
> 2 1 null
> 3 2 (1, 2)
> 4 2 (1, 2)
> 5 3 (1, 2, 3, 4)
> 6 3 (1, 2, 3, 4)
> 7 4 (3, 4, 5, 6)
> 8 4 (3, 4, 5, 6)
> rows (ordered): 8
SELECT *, ARRAY_AGG(ID) OVER (ORDER BY VALUE RANGE BETWEEN 1 FOLLOWING AND 2 FOLLOWING) FROM TEST;
> ID VALUE ARRAY_AGG(ID) OVER (ORDER BY VALUE RANGE BETWEEN 1 FOLLOWING AND 2 FOLLOWING)
> -- ----- -----------------------------------------------------------------------------
> 1 1 (3, 4, 5, 6)
> 2 1 (3, 4, 5, 6)
> 3 2 (5, 6, 7, 8)
> 4 2 (5, 6, 7, 8)
> 5 3 (7, 8)
> 6 3 (7, 8)
> 7 4 null
> 8 4 null
> rows (ordered): 8
DROP TABLE TEST;
> ok
......@@ -139,8 +139,8 @@ SELECT ID, CATEGORY,
NTH_VALUE(CATEGORY, 2) OVER (ORDER BY CATEGORY RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) C,
NTH_VALUE(CATEGORY, 2) OVER (ORDER BY CATEGORY RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW EXCLUDE CURRENT ROW)
FROM TEST FETCH FIRST 3 ROWS ONLY;
> ID CATEGORY C NTH_VALUE(CATEGORY, 2) OVER (ORDER BY CATEGORY RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW EXCLUDE CURRENT ROW)
> -- -------- ---- ---------------------------------------------------------------------------------------------------------------------
> ID CATEGORY C NTH_VALUE(CATEGORY, 2) OVER (ORDER BY CATEGORY RANGE UNBOUNDED PRECEDING EXCLUDE CURRENT ROW)
> -- -------- ---- ---------------------------------------------------------------------------------------------
> 1 1 null null
> 2 1 1 null
> 3 1 1 1
......
Markdown 格式
0%
您添加了 0 到此讨论。请谨慎行事。
请先完成此评论的编辑!
注册 或者 后发表评论