/*
* Copyright 2004-2011 H2 Group. Multiple-Licensed under the H2 License,
* Version 1.0, and under the Eclipse Public License, Version 1.0
* (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.expression;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import org.h2.engine.Database;
import org.h2.engine.Session;
import org.h2.message.DbException;
import org.h2.table.Column;
import org.h2.table.ColumnResolver;
import org.h2.table.TableFilter;
import org.h2.util.StringUtils;
import org.h2.value.DataType;
import org.h2.value.Value;
import org.h2.value.ValueArray;
/**
* An expression is a operation, a value, or a function in a query.
*/
public abstract class Expression {
private boolean addedToFilter;
/**
* Return the resulting value for the current row.
*
* @param session the session
* @return the result
*/
public abstract Value getValue(Session session);
/**
* Return the data type. The data type may not be known before the
* optimization phase.
*
* @return the type
*/
public abstract int getType();
/**
* Map the columns of the resolver to expression columns.
*
* @param resolver the column resolver
* @param level the subquery nesting level
*/
public abstract void mapColumns(ColumnResolver resolver, int level);
/**
* 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 scale of this expression.
*
* @return the scale
*/
public abstract int getScale();
/**
* Get the precision of this expression.
*
* @return the precision
*/
public abstract long getPrecision();
/**
* Get the display size of this expression.
*
* @return the display size
*/
public abstract int getDisplaySize();
/**
* Get the SQL statement of this expression.
* This may not always be the original SQL statement,
* specially after optimization.
*
* @return the SQL statement
*/
public abstract String getSQL();
/**
* 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
*/
public abstract void updateAggregate(Session session);
/**
* 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(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;
}
/**
* 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, false, or null.
* 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
*/
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 StringUtils.unEnclose(getSQL());
}
/**
* Only returns true if the expression is a wildcard.
*
* @return if this expression is a wildcard
*/
public boolean isWildcard() {
return false;
}
/**
* 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
* @param outerJoin if the expression is part of an outer join
*/
public void addFilterConditions(TableFilter filter, boolean outerJoin) {
if (!addedToFilter && !outerJoin && isEverything(ExpressionVisitor.EVALUATABLE_VISITOR)) {
filter.addFilterCondition(this, false);
addedToFilter = true;
}
}
/**
* Convert this expression to a String.
*
* @return the string representation
*/
public String toString() {
return getSQL();
}
/**
* If this expression consists of column expressions it should return them.
*
* @param session the session
* @return array of expression columns if applicable, null otherwise
*/
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
*/
static Expression[] getExpressionColumns(Session session, ValueArray 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(), v.getPrecision(), v.getScale(),
v.getDisplaySize());
expr[i] = new ExpressionColumn(session.getDatabase(), col);
}
return expr;
}
/**
* Extracts expression columns from the given result set.
*
* @param session the session
* @param rs the result set
* @return an array of expression columns
*/
public static Expression[] getExpressionColumns(Session session, ResultSet rs) {
try {
ResultSetMetaData meta = rs.getMetaData();
int columnCount = meta.getColumnCount();
Expression[] expressions = new Expression[columnCount];
Database db = session == null ? null : session.getDatabase();
for (int i = 0; i < columnCount; i++) {
String name = meta.getColumnLabel(i + 1);
int type = DataType.convertSQLTypeToValueType(meta.getColumnType(i + 1));
int precision = meta.getPrecision(i + 1);
int scale = meta.getScale(i + 1);
int displaySize = meta.getColumnDisplaySize(i + 1);
Column col = new Column(name, type, precision, scale, displaySize);
Expression expr = new ExpressionColumn(db, col);
expressions[i] = expr;
}
return expressions;
} catch (SQLException e) {
throw DbException.convert(e);
}
}
}