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/*
* Copyright 2004-2019 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.expression;
import java.util.List;
import org.h2.engine.Database;
import org.h2.engine.Session;
import org.h2.result.ResultInterface;
import org.h2.table.Column;
import org.h2.table.ColumnResolver;
import org.h2.table.TableFilter;
import org.h2.value.TypeInfo;
import org.h2.value.Value;
import org.h2.value.ValueCollectionBase;
/**
* An expression is a operation, a value, or a function in a query.
*/
public abstract class Expression {
/**
* Initial state for {@link #mapColumns(ColumnResolver, int, int)}.
*/
public static final int MAP_INITIAL = 0;
/**
* State for expressions inside a window function for
* {@link #mapColumns(ColumnResolver, int, int)}.
*/
public static final int MAP_IN_WINDOW = 1;
/**
* State for expressions inside an aggregate for
* {@link #mapColumns(ColumnResolver, int, int)}.
*/
public static final int MAP_IN_AGGREGATE = 2;
private boolean addedToFilter;
/**
* Get the SQL snippet for a list of expressions.
*
* @param builder the builder to append the SQL to
* @param expressions the list of expressions
* @param alwaysQuote quote all identifiers
*/
public static void writeExpressions(StringBuilder builder, List expressions,
boolean alwaysQuote) {
for (int i = 0, length = expressions.size(); i < length; i++) {
if (i > 0) {
builder.append(", ");
}
expressions.get(i).getSQL(builder, alwaysQuote);
}
}
/**
* Get the SQL snippet for an array of expressions.
*
* @param builder the builder to append the SQL to
* @param expressions the list of expressions
* @param alwaysQuote quote all identifiers
*/
public static void writeExpressions(StringBuilder builder, Expression[] expressions, boolean alwaysQuote) {
for (int i = 0, length = expressions.length; i < length; i++) {
if (i > 0) {
builder.append(", ");
}
Expression e = expressions[i];
if (e == null) {
builder.append("DEFAULT");
} else {
e.getSQL(builder, alwaysQuote);
}
}
}
/**
* Return the resulting value for the current row.
*
* @param session the session
* @return the result
*/
public abstract Value getValue(Session session);
/**
* Returns the data type. The data type may not be known before the
* optimization phase.
*
* @return the data type
*/
public abstract TypeInfo getType();
/**
* Map the columns of the resolver to expression columns.
*
* @param resolver the column resolver
* @param level the subquery nesting level
* @param state current state for nesting checks, initial value is
* {@link #MAP_INITIAL}
*/
public abstract void mapColumns(ColumnResolver resolver, int level, int state);
/**
* Try to optimize the expression.
*
* @param session the session
* @return the optimized expression
*/
public abstract Expression optimize(Session session);
/**
* Tell the expression columns whether the table filter can return values
* now. This is used when optimizing the query.
*
* @param tableFilter the table filter
* @param value true if the table filter can return value
*/
public abstract void setEvaluatable(TableFilter tableFilter, boolean value);
/**
* Get the SQL statement of this expression.
* This may not always be the original SQL statement,
* specially after optimization.
*
* @param alwaysQuote quote all identifiers
* @return the SQL statement
*/
public String getSQL(boolean alwaysQuote) {
return getSQL(new StringBuilder(), alwaysQuote).toString();
}
/**
* Appends the SQL statement of this expression to the specified builder.
* This may not always be the original SQL statement, specially after
* optimization.
*
* @param builder
* string builder
* @param alwaysQuote quote all identifiers
* @return the specified string builder
*/
public abstract StringBuilder getSQL(StringBuilder builder, boolean alwaysQuote);
/**
* Appends the SQL statement of this expression to the specified builder.
* This may not always be the original SQL statement, specially after
* optimization. Enclosing '(' and ')' are removed.
*
* @param builder
* string builder
* @param alwaysQuote
* quote all identifiers
* @return the specified string builder
*/
public StringBuilder getUnenclosedSQL(StringBuilder builder, boolean alwaysQuote) {
int first = builder.length();
int last = getSQL(builder, alwaysQuote).length() - 1;
if (last > first && builder.charAt(first) == '(' && builder.charAt(last) == ')') {
builder.setLength(last);
builder.deleteCharAt(first);
}
return builder;
}
/**
* Update an aggregate value. This method is called at statement execution
* time. It is usually called once for each row, but if the expression is
* used multiple times (for example in the column list, and as part of the
* HAVING expression) it is called multiple times - the row counter needs to
* be used to make sure the internal state is only updated once.
*
* @param session the session
* @param stage select stage
*/
public abstract void updateAggregate(Session session, int stage);
/**
* Check if this expression and all sub-expressions can fulfill a criteria.
* If any part returns false, the result is false.
*
* @param visitor the visitor
* @return if the criteria can be fulfilled
*/
public abstract boolean isEverything(ExpressionVisitor visitor);
/**
* Estimate the cost to process the expression.
* Used when optimizing the query, to calculate the query plan
* with the lowest estimated cost.
*
* @return the estimated cost
*/
public abstract int getCost();
/**
* If it is possible, return the negated expression. This is used
* to optimize NOT expressions: NOT ID>10 can be converted to
* ID<=10. Returns null if negating is not possible.
*
* @param session the session
* @return the negated expression, or null
*/
public Expression getNotIfPossible(@SuppressWarnings("unused") Session session) {
// by default it is not possible
return null;
}
/**
* Check if this expression will always return the same value.
*
* @return if the expression is constant
*/
public boolean isConstant() {
return false;
}
/**
* Check if this expression will always return the NULL value.
*
* @return if the expression is constant NULL value
*/
public boolean isNullConstant() {
return false;
}
/**
* Is the value of a parameter set.
*
* @return true if set
*/
public boolean isValueSet() {
return false;
}
/**
* Check if this is an auto-increment column.
*
* @return true if it is an auto-increment column
*/
public boolean isAutoIncrement() {
return false;
}
/**
* Get the value in form of a boolean expression.
* Returns true or false.
* In this database, everything can be a condition.
*
* @param session the session
* @return the result
*/
public boolean getBooleanValue(Session session) {
return getValue(session).getBoolean();
}
/**
* Create index conditions if possible and attach them to the table filter.
*
* @param session the session
* @param filter the table filter
*/
@SuppressWarnings("unused")
public void createIndexConditions(Session session, TableFilter filter) {
// default is do nothing
}
/**
* Get the column name or alias name of this expression.
*
* @return the column name
*/
public String getColumnName() {
return getAlias();
}
/**
* Get the schema name, or null
*
* @return the schema name
*/
public String getSchemaName() {
return null;
}
/**
* Get the table name, or null
*
* @return the table name
*/
public String getTableName() {
return null;
}
/**
* Check whether this expression is a column and can store NULL.
*
* @return whether NULL is allowed
*/
public int getNullable() {
return Column.NULLABLE_UNKNOWN;
}
/**
* Get the table alias name or null
* if this expression does not represent a column.
*
* @return the table alias name
*/
public String getTableAlias() {
return null;
}
/**
* Get the alias name of a column or SQL expression
* if it is not an aliased expression.
*
* @return the alias name
*/
public String getAlias() {
return getUnenclosedSQL(new StringBuilder(), false).toString();
}
/**
* Returns the main expression, skipping aliases.
*
* @return the expression
*/
public Expression getNonAliasExpression() {
return this;
}
/**
* Add conditions to a table filter if they can be evaluated.
*
* @param filter the table filter
*/
public void addFilterConditions(TableFilter filter) {
if (!addedToFilter && isEverything(ExpressionVisitor.EVALUATABLE_VISITOR)) {
filter.addFilterCondition(this, false);
addedToFilter = true;
}
}
/**
* Convert this expression to a String.
*
* @return the string representation
*/
@Override
public String toString() {
return getSQL(false);
}
/**
* If this expression consists of column expressions it should return them.
*
* @param session the session
* @return array of expression columns if applicable, null otherwise
*/
@SuppressWarnings("unused")
public Expression[] getExpressionColumns(Session session) {
return null;
}
/**
* Extracts expression columns from ValueArray
*
* @param session the current session
* @param value the value to extract columns from
* @return array of expression columns
*/
protected static Expression[] getExpressionColumns(Session session, ValueCollectionBase value) {
Value[] list = value.getList();
ExpressionColumn[] expr = new ExpressionColumn[list.length];
for (int i = 0, len = list.length; i < len; i++) {
Value v = list[i];
Column col = new Column("C" + (i + 1), v.getType());
expr[i] = new ExpressionColumn(session.getDatabase(), col);
}
return expr;
}
/**
* Extracts expression columns from the given result set.
*
* @param session the session
* @param result the result
* @return an array of expression columns
*/
public static Expression[] getExpressionColumns(Session session, ResultInterface result) {
int columnCount = result.getVisibleColumnCount();
Expression[] expressions = new Expression[columnCount];
Database db = session == null ? null : session.getDatabase();
for (int i = 0; i < columnCount; i++) {
String name = result.getColumnName(i);
TypeInfo type = result.getColumnType(i);
Column col = new Column(name, type);
Expression expr = new ExpressionColumn(db, col);
expressions[i] = expr;
}
return expressions;
}
/**
* Returns count of subexpressions.
*
* @return count of subexpressions
*/
public int getSubexpressionCount() {
return 0;
}
/**
* Returns subexpression with specified index.
*
* @param index 0-based index
* @return subexpression with specified index, may be null
* @throws IndexOutOfBoundsException if specified index is not valid
*/
public Expression getSubexpression(int index) {
throw new IndexOutOfBoundsException();
}
}
